The Constitution, Invasion, Immigration, and the War Powers of States

Recent events at the southern border of the United States have raised controversy about whether, and to what extent, states may respond without federal cooperation. Central to the controversy are two constitutional questions: (1) Upon ratification of the Constitution, did any state sovereign war powers survive, or was all such authority ceded to the federal government? and (2) if any state war powers did survive, what is their scope?

Thus far, scholarship and Supreme Court jurisprudence have provided no clear answers to those questions.

One of the few, and perhaps the only, law journal article dedicated to state war powers is a student comment: Heather Dwyer, The State War Power: A Forgotten Constitutional Clause, 33 U. La Verne L. Rev. 319, 320 (2012) (claiming the existence of a “Constitutionally derived State War Power”). Outside the realm of formal scholarship is Mark Brnovich, The Federal Government’s Duty to Protect the States and the State’s Sovereign Power of Self Defense When Invaded, Op. Ariz. A.G. No. I22-001 (Feb. 27, 2022), http://perma.cc/EBG8-VZ9D (concluding that certain activities at the southern border qualify as an “invasion” as the Constitution uses the term); Joshua Treviño, Tex. Pub. Pol. Inst., The Meaning of Invasion Under the Compact Clause of the U.S. Constitution (2022), https://www.texaspolicy.com/wp-content/uploads/2022/11/2022-11-RR-SST-CompactClause-JoshuaTrevino-paper5-.pdf (concluding that certain activities at the southern border qualify as an “invasion” as the Constitution uses the term).

Nearly all the leading Founders had been born and raised under the British flag—either in the North American colonies, Britain, Ireland, or (as in the case of Alexander Hamilton) the British Caribbean. Understanding the Constitution they adopted requires some information on the empire they had inhabited.

The island of Great Britain consisted (as it still consists today) of England, Wales, and Scotland. England and Wales had been united for legal purposes in the sixteenth century. The English and Scottish Crowns were conjoined upon the accession of James I in 1603, but England and Scotland remained separate kingdoms, each with its own parliament. Then in 1707, both parliaments passed Acts of Union, thereby creating the Kingdom of Great Britain with a common British Parliament. Within those limitations, Scotland retained its own legal system, as it does today.

Scotland recovered its own parliament in 1999.

After the territorial losses from the American Revolution, the Empire encompassed the following territories: the island of Great Britain along with small nearby islands, Ireland, Canada, much of India, Bermuda, an incipient colony in and near Australia, and valuable Caribbean islands, including the Bahamas, Jamaica, and Trinidad.

Most colonies enjoyed at least some degree of self-governance, but they usually fashioned their institutions from English (rather than Scottish or Irish) models. Some core legal concepts (such as “allegiance,” discussed below in Part IV), were common to the entire empire.

As might be expected, the Constitution’s language and structure were influenced heavily by English jurisprudence.

Robert G. Natelson, Did the Constitution Grant the Federal Government Eminent Domain Power? Using Eighteenth Century Law to Answer Constitutional Questions, 19 Fed. Soc’y Rev. 88 (2018).

To assist in reconstructing the Constitution’s meaning, we draw heavily on the European “law of nations” treatises and on Anglo-American case reports, law dictionaries, digests, and other legal works used by Founding-era lawyers. We also draw on contemporaneous lay dictionaries and other literary sources.

Courts and lawyers typically refer to Article I, Section 10 of the Constitution as the Compact Clause and Article IV, Section 4 as the Guarantee Clause. Our examination, however, focuses only on selected components of those two provisions. To increase precision, we identify the relevant components as follows: The Self-Defense Clause is the part of the Compact Clause that provides, “No State shall, without the Consent of Congress . . . keep Troops, or Ships of War in time of Peace . . . or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.

U.S. Const. art. I, § 10, cl. 3; cf. United States v. Abbott, No. 1:23-CV-853-DAE, slip op. at 31 (W.D. Tex. Sep. 6, 2023).

The Founders’ international law authorities recognized that the term “war” could describe episodes of combat, but for legal purposes they defined it as a continuous state or condition. Hugo Grotius defined war as “the State or Situation of those . . . who Dispute by Force of Arms.”

1 Grotius, supra note 3, at 134.

Wars were classified as private, public, or mixed.

1 Grotius, supra note 3, at 240 (“Mixed war is that which is made on one Side by publick Authority, and on the other by mere private Persons.”).

A war could be offensive and just, offensive and unjust, defensive and just, or—in rare cases—defensive and unjust.

2 Vattel, supra note 3, at 35 (“[B]ut this is a case very rarely known among nations. There are few defensive wars without at least some apparent reason for warranting their justice and necessity”).

A defensive war was one waged to prevent injury.

1 Vattel, supra note 3, at 143 (“[T]he right of a just defence, which belongs to every nation; or the right of making use of force against whoever attacks it, and its privileges. This is the foundation of a defensive war.”).

Offensive wars were fought to seek compensation for perceived injury or to deter the enemy from inflicting anticipated injury.

1 Vattel, supra note 3, at 143 (“the right to obtain justice by force, if we cannot obtain it otherwise, or to pursue our right by force of arms. This is the foundation of an offensive war”).

Under the law of nations, only a sovereign was privileged to make war or to delegate the power to do so.

2 Vattel, supra note 3, at 2 (“Thus the sovereign power has alone authority to make war”).

Initiation of hostilities might be signaled by a declaration of war—sometimes called a “denunciation,” after denuntio, the Latin word for a declaration of war. A declaration was not required for a defensive war, but was expected for an offensive one.

2 Vattel, supra note 3, at 22–23. But see The Federalist No. 25, N.Y. Packet, Dec. 21, 1787 (Alexander Hamilton), reprinted in 15 Documentary History, supra note 3, at 62 (claiming that “the ceremony of a formal denunciation of war has of late fallen into disuse”). Hamilton’s conclusion is buttressed by Georg Friedrich Martens, whose international law treatise was composed in French contemporaneously with the Constitution’s adoption, but not translated into English until 1795. Georg Friedrich von Martens, Summary of the Law of Nations 274 (Wm. Cobbett trans., 1795) (“The universal law of nations acknowledges no general obligation of making a declaration of war to the enemy, previous to the commencement of hostilities”). A declaration “to the enemy” must be distinguished from one directed at all or some of the sovereign’s own people.

A just war empowered the sovereign to undertake nearly all means necessary to accomplish its purpose of preventing or repairing injury or forestalling future injury.

2 Vattel, supra note 3, at 47–48:

For when the end is lawful, he who has a right to prosecute this end is warranted in the use of all necessary means to attain it . . . On a declaration of war, therefore, this nation has a right of doing against the enemy whatever is necessary to this justifiable end of bringing him to reason, and obtaining justice and security from him.

Besides killing enemies who refuse to surrender their arms, a belligerent could capture them,

Id.

Eighteenth century war was often a brutal exercise

Dennis Showalter, Matrices: Soldiers and Civilians in Early Modern Europe, 1648–1789, in Daily Lives of Civilians in Wartime Europe, 1618–1900 at 58, 83 (Linda S. Frey & Marshal L. Frey eds., 2007) (describing armies’ devastation of areas of Europe.

These authorities on the law of nations also laid down the rule that a belligerent should not pursue, seize, or kill enemies in a neutral country.

3 Grotius, supra note 3, at 1282; 1 Vattel, supra note 3, at 151.

Founding-era international law identified persons engaged in particularly reprehensible activities outside ties of national allegiance as “enemies of the human race”—hostes humani generis.

The concept of “enemy of the human race” appears in a 358 C.E. decree of the Roman Emperor Constantius II. The Empire’s rulers were then Christian, and they disapproved of magicians: homines magi, in quacumque sint parte terrarum, humani generis inimici credendi sunt. Code Just. 9.18.7pr (Constantius II 358) (“Magicians in whatever part of the world they may be, must be believed to be enemies of the human race.”) This decree used the word inimicus for “enemy,” not hostis, the Founding-era appellation for an alien enemy. By 1736, sorcery prosecutions had ceased in England. Owen Davies. Witchcraft, Magic and Culture, 1736–1951 at 79, 91 (1999).

Wars against enemies of the human race were always just.

2 Grotius, supra note 3, at 1022–23 (proclaiming war just against pirates and assorted other malefactors).

A nation capturing enemies of the human race had the choice of treating them as prisoners of war or as common criminals. William Blackstone argued for their being treated as criminals rather than as prisoners of war in the first volume of his Commentaries.

1 William Blackstone, Commentaries *249; see also Calvin’s Case (1608) 77 Eng. Rep. 377, 406; 7 Co. Rep. 1, 24b (K.B.) (accounting proditores (traitors) and praedones (pirates) as excluded from formal enemies in war).

Treating captured hostes humani generis as accused criminals denied them the honorable status of prisoners of war normally accorded captured enemy aliens. Treating them as captured enemy aliens, on the other hand, denied them privileges—such as trial by jury—to which accused criminals were entitled.

The concept of “allegiance” also defined the scope of permissible conduct during war. This subject is addressed in Part IV.

The charters of the North American colonies typically granted them authority to wage defensive war. For example, the 1629 royal charter for Massachusetts Bay colony provided in part:

AND WEE [i.e., the king] DOE further . . . give and graunte to the said Governor and Company, and their Successors, by theis Presents, that it shall and maie be lawfull . . . to incounter, expulse, repell, and resist by Force of Armes, as well by Sea as by Lande, and by all fitting Waies and Meanes whatsoever, all such Person and Persons, as shall at any Tyme hereafter, attempt or enterprise the Destruccon, Invasion, Detriment, or Annoyaunce to the said Plantation or Inhabitants . . .

Mass. Charter (1629), https://avalon.law.yale.edu/17th_century/mass03.asp. See also R.I. Charter (1663), https://avalon.law.yale.edu/17th_century/ri04.asp (wording similar to Massachusetts Bay); Conn. Charter (1662), https://avalon.law.yale.edu/17th_century/ct03.asp (granting power to defend against the “Destruction, Invasion, Detriment, or Annoyance of the said Inhabitants or Plantation”); Ga. Charter (1732), https://avalon.law.yale.edu/18th_century/ga01.asp (granting military power to respond to “destruction, invasion, detriment or annoyance of our said colony”); Md. Charter (1632), https://avalon.law.yale.edu/17th_century/ma01.asp (granting power to “build and fortify Castles, Forts, and other Places of Strength . . . for the Public and their own Defence”). See also Carolina Charter (1663), https://avalon.law.yale.edu/17th_century/nc01.asp:

[W]e . . . do give power . . . to levy, muster and train all sorts of men, of what condition or wheresoever born, in the said province for the time being, and to make war and pursue the enemies aforesaid, as well by sea as by land, yea, even without the limits of the said province, and by God’s assistance to vanquish and take them, and being taken to put them to death by the law of war, or to save them at their pleasure; and to do all and every other thing, which unto the charge of a captain general of an army belongeth, or hath accustomed to belong, as fully and freely as any captain general of an army hath or ever had the same.

Although several charters authorized the grantees to oppose anyone seeking their “destruction, invasion, detriment, or annoyance,” we caution against inferring from the canon noscitur a sociis that, for example, all elements in this list require adversarial confrontation. An invasion can occur without initial confrontation and without destruction; infra Part III (E); conversely, destructuon and destruction (via a blockade, for example) can occur without invasion.

When the Declaration of Independence was issued, the thirteen colonies signing the document became states. They thereby assumed as a matter of sovereign right what previously had been a subject of grant. Thus, under both the Articles of Confederation and the Constitution, the source of most state authority

“Most” because the Constitution does grant a few specific powers to the states. Robert G. Natelson, Federal Functions: Execution of Powers the Constitution Grants to Persons and Entities Outside the Federal Government, 23 U. Penn. J. Const. L. 193 (2021) (describing the Constitution’s grants of specific powers to states and other entities).

To be sure, the controversial “doctrine of inherent sovereign authority” holds that the states never enjoyed power over military and other foreign affairs subjects, and that the federal government received that authority directly from its congressional predecessors—thereby bypassing the Articles and the Constitution entirely.

The leading statement of this doctrine appears in United States v. Curtiss-Wright Corp., 299 U.S. 304 (1936).

As the North Atlantic Treaty was to do 168 years later,

The North Atlantic Treaty, Apr. 4, 1949, 63 Stat. 2241, 34 U.N.T.S. 243, https://www.nato.int/cps/en/natohq/official_texts_17120.htm (creating, among other obligations, mutual assistance in case of an attack on any member and creating the North Atlantic Council as an administering body). For an explanation of why the Articles of Confederation created, rather than a true constitution, a treaty or league somewhat comparable to NATO, see Natelson, supra note 72, at 362–65.

The upshot was that the states retained virtually unlimited flexibility to engage in defensive land war—even after Congress had been consulted—except for power to strike preemptively at non-Indian enemies. Their naval scope was more constricted: They could maintain navies to fight congressionally-declared wars. They could issue letters of marque and reprisal only against congressionally-declared enemies. They could maintain fleets and launch them to suppress pirates, although limited by congressional review.

As for other powers related to war, the states retained authority to limit foreign immigration, impose embargoes, and suspend the writ of habeas corpus. However, state treaties and alliances were subject to congressional review, and state imposts and duties had to be consistent with congressional treaties.

Supra note 74.

Founding-era international law scholars acknowledged each nation’s prerogative of dividing war powers among different administrative levels.

Supra note 29 and accompanying text.

The Protection From Invasion Clause and the Domestic Violence Clause imposed duties on the federal government to wage defensive war under certain circumstances: “The United States . . . shall protect each [state] . . . against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.”

U.S. Const. art. IV, § 4 (“The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.”).

The Take Care Clause

U.S. Const. art. II, § 3. One of us (Hyman) believes the Take Care Clause was only an authorization to wage defensive war if Congress has not enacted valid legislation to the contrary, and if (furthermore) the President seeks only to maintain the operation of federal law rather than state law, using tools lawfully at his disposal.

In addition, the Define and Punish Clause deputized Congress to “define and punish Piracies and Felonies committed on the High Seas.”

Id. I, § 8, cl. 10.

Other enumerated powers granted Congress the means to wage war. Congress could: -

“grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;”

U.S. Const. art. I, § 8, cl. 11.

In addition, the Constitution granted Congress and the President certain powers wholly or partly associated with war. Specifically, the Constitution— -

conferred on the President, with the advice and consent of the Senate, sole authority to make treaties;

U.S. Const. art. II, § 2, cl. 2

To the extent the Constitution did not qualify them, war powers remained in the states by reservation.

2 Farrand, supra note 3, at 332 (Aug. 18, 1787) (Madison, reporting Roger Sherman as saying, “the States might want their Militia for defence agst invasions and insurrections, and for enforcing obedience to their laws. They will not give up this point”).

The Constitution’s opponents objected that this clause gave Congress exclusive power over state militias. But the Constitution’s advocates pointed out that the opponents were overlooking state reserved powers. The future Chief Justice John Marshall explained:

The State Legislatures had power to command and govern their militia before, and have it still, undeniably, unless there be something in this Constitution that takes it away …. All the restraints intended to be laid on the State Governments (besides where an exclusive power is expressly given to Congress) are contained in the tenth section, of the first article. This power is not included in the restrictions in that section.—But what excludes every possibility of doubt, is the last part of it.—That “no State shall engage in war, unless actually invaded, or in such imminent danger as will not admit of delay.” When invaded, they can engage in war; as also when in imminent danger. This clearly proves, that the States can use the militia when they find it necessary.

Debates of the Virginia Convention (Jun. 16, 1788) in 10 Documentary History, supra note 3, at 1307 (comments of John Marshall). See also note 118 infra (quoting more of Marshall’s speech). Modern commentators sometimes overlook the role of the militia in defending a state from invasion. E.g., Robert Leider, The Modern Militia (2023), https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4362391 (listing three purposes of the militia, but not its role in state defense).

Marshall’s analysis was reinforced by James Madison

Debates of the Virginia Convention (Jun. 16, 1788) in 10 Documentary History, supra note 3, at 1273 & 1311 (comments of James Madison).

The Constitution limited and qualified reserved state war powers in several respects. The result was a balance between federal and state prerogatives roughly similar to that under the Articles of Confederation. But in one way the Constitution constricted the states’ war powers further, and in four ways it actually expanded them.

The Articles had permitted states to maintain naval vessels in peacetime up to a congressionally-prescribed maximum. The Constitution provided, “No State shall, without the Consent of Congress . . . keep . . . Ships of War in time of Peace.”

U.S. Const. art. I, § 10, cl. 3.

The states’ sole loss of war power was on the naval side. This was the Constitution’s removal of their prerogative to issue letters of marque or reprisal against an enemy upon whom Congress had declared war.

Id. cl. 1 (“No State shall . . . grant letters of marque and reprisal . . .”). Letters of marque and reprisal allowed private ships to attack ships of a target nationality, and seize them or their belongings.

The increases in state war powers were as follows: First, the Constitution did not require a congressional declaration of war for states to build ships. It required only war de facto, with no requirement that the war be one waged by the federal government. Second, the Constitution deprived Congress of its veto over state naval actions against invading pirates.

Third, on the land side, the Constitution preserved general state control over their militias while providing that “No State shall, without the Consent of Congress . . . keep Troops . . . in time of Peace . . . or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.”

Id. cl. 3.

Fourth, while the Articles had permitted state preemptive strikes against imminent invasions by Indians only, the Constitution permitted them against all invasions.

The states also retained unmentioned prerogatives sometimes associated with war. As participants in the ratification debates observed, states would continue to have power to suspend the writ of habeas corpus.

Debates of the Massachusetts Convention (Jan. 26, 1788) in 6 Documentary History, supra note 3, at 1359 (comments of Samuel Adams: “this power, given to the general government to suspend this privilege in cases. of rebellion and invasion, did not take away the power of the several States to suspend it, if they see fit”); Luther Martin, Genuine Information VIII, Baltimore Md. Gazette, Jan. 22, 1788, reprinted in 15 Documentary History, supra note 3, at 433, 434 (“the State governments have a power of suspending the habeas corpus act”).

Some readers may find the conclusion that the states retained significant military authority to be counterintuitive. In part, this may be due to the fact that the states rarely exercise such authority today. In part, also, it may be due to the general conception of the Constitution as uniformly increasing central power.

The truth, however, is more complicated. In negotiating the constitutional re-arrangement, the states sometimes gained as well as lost, and military affairs may not be the only case of this happening.

Arguably Indian affairs was another area. Under the Articles of Confederation, Congress enjoyed plenary authority over Indians outside state boundaries. Under the Constitution, Congress’s authority was limited to the scope of its enumerated powers. Robert G. Natelson, The Original Understanding of the Indian Commerce Clause, 85 Denver U. L. Rev. 201 (2007). Claims such as that made in Haaland v. Brackeen, 599 U.S. 255, 273 (2023), that the Indian Commerce Clause, U.S. Const. art. I, § 8, cl. 3, somehow granted Congress nearly plenary authority over Indian affairs, are not supported by the historical record. See generally Robert G. Natelson, The Original Understanding of the Indian Commerce Clause: An Update, 23 Federalist Soc’y Rev. 209 (2022).

Additionally, curbing state prerogatives and strengthening the central power were not the only reasons for the Constitution. The Founders also sought to protect the states, to prevent them from degenerating into monarchy or anarchy, and to improve the quality of their governance. All these policies are evident in the first sentence of Article IV, Section 4.

U.S. Const. art. IV, § 4 (“The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.”). See Robert G. Natelson, Guarantee Clause, in The Heritage Guide to the Constitution 368–370 (David F. Forte & Matthew Spalding eds., 2d ed. 2014) (discussing the reasons for the clause).

The words invade and invasion served as triggers for both federal and state defensive war powers. Thus, the Constitution’s Calling Forth Clause empowered Congress to enlist state militias in federal service “to execute the Laws of the Union, suppress Insurrections and repel Invasions.”

U.S. Const. art. I, § 8, cl. 15. (Italics added).

In Perpich v. Dept. of Defense, 496 U.S. 334 (1990), the Supreme Court held that the National Guard can be federalized also through the congressional power to “raise and support armies,” U.S. Const. art. I, § 8, cl. 12, and then used for whatever purposes the federal government may use armies. The authors find this interpretation of the constitutional text problematic. Under the expressio unius est exclusio alterius maxim, the Constitution’s list of three grounds (in the Calling Forth Clause) for federalizing the state militias should be exclusive.

This construction is reinforced by the modern non-commandeering doctrine and by comments from advocates of the Constitution during the ratification debates. See, e.g., Debates of the Virginia Convention, 10 Documentary History, supra note 3, at 1307 (comments of John Marshall: “For Continental purposes Congress may call forth the militia; as to suppress insurrections and repel invasions. But the power given to the States by the people is not taken away”). See also supra notes 103–107.

In any event, during a defensive war the state still may raise “Troops” other than its militia. U.S. Const. art. I, § 10, cl. 3. Moreover, part of the state militia is the “sedentary militia,” which consists of almost all “males age eighteen to forty-five [and is] protected against federal interference by the Second Amendment….” Glenn Reynolds & Don Kates, The Second Amendment and States’ Rights, 36 Wm. & Mary L. Rev. 1737, 1761 (1995).

During the eighteenth century, “invasion” and its variants in their broadest sense could include infringements or attacks on rights and privileges—as in the phrase, “The censorship policy was an invasion of the right of free speech.”

E.g., “A Citizen of Philadelphia,” The Weaknesses of Brutus Exposed, Nov. 8, 1787 reprinted in 14 Documentary History, supra note 3, at 63, 71 (“The unceasing cry of these designing croakers is, my friends, your liberty is invaded!”); cf. The Declaration of Independence, para. 7 (“his invasions on the rights of the people”).

But what kind of incursion? Is the meaning limited to intrusion by a foreign army? Several Court of Appeals opinions have said as much, but on very sparse evidence.

California v. United States, 104 F.3d 1086, 1091 (9^th Cir. 1997); Padavan v. United States, 83 F.3d 23, 28 (2d Cir. 1996); New Jersey v. United States, 91 F.3d 463, 468 (3d Cir. 1996) (all interpreting “invasion” as limited to an incursion by a foreign army).

Eighteenth-century dictionaries inform us that when “invasion” and its variants applied to physical intrusions, the scope was not limited to incursions by a foreign army. Among the thirteen Founding-era English dictionaries we examined, only one seemed to limit “invasion” and its variants to formal military operations.

Thomas Dyche & William Pardon, A New General English Dictionary (16^th ed. 1777) (unpaginated), defining “invade” as

to come violently, illegally, unfairly, or unjustly, into the lands, possessions, or country of another; and is commonly understood of the army of one nation coming suddenly and unprovoked into another’s kingdome [sic] or country, and keeping possession of all or part thereof by violence, or driving away the cattle, making prisoners of the people, or doing other acts of hostility.

The same source defined “invasion” as “the violent, sudden, and illegal entering of an army, &c. into another’s country and keeping possession, or committing hostilities.” Id.

The reader may observe that some of these definitions required that an invasion be “hostile.” For that reason, we included in footnote 125 the entry for “hostile” from each dictionary employing that word when defining “invasion” or its variants. As those entries show, “hostile” often meant merely “adverse.” Readers may recognize this as the non-military definition preserved in the modern law of adverse possession and in legal phrases such as “hostile takeover” and “hostile witness.” Thus, all we can infer from the requirement of “hostility” is that for an entry to be an invasion it must be unauthorized and uninvited.

Eighteenth-century American political discourse confirms what the dictionaries suggest: the scope of “invasion” and its variants was quite broad.

First: An invasion could be by sea as well as by land. Both the congressional records

30 JCC, supra note 3, at 447 (Jul. 31, 1786) (“That in case of an invasion of any of the middle or eastern states by a marine power the possession of Hudson’s River would be an object of the highest importance as well to the invader as to the United States.”).

Second: An invasion need not be incident to actual warfare, nor an operation of war. The Massachusetts Constitution of 1780, for example, spoke of “time of war or invasion” (and it still does).

Mass. Const., Part the Second, chap. II, § 1, art. VII. (Italics added). See also infra notes 134 and 141. This does not imply, of course, that warfare cannot be used to counter an invasion not incident to war; nor does it mean that “peaceful” invaders are not in “enmity.”

Third: An invasion need not be launched by a formal military force. Participants in the constitutional debates referred to “invasions of barbarous tribes,”

Charles Carroll of Carrollton, Draft Speech for Maryland Convention, Jan.–Mar., 1788, in 12 Documentary History, supra note 3, at 832, 856.

An “invasion” could refer also to uninvited entry by groups of immigrants.

Because of its insular position, Britain did not need to defend its border against unauthorized crossing by land. But Britain faced similar issues on the coast. Thus, a 1758 essay discussed “invasion by a fleet of unarmed flat-bottomed boats,” although denying that the problem was serious enough to justify a large navy. Number CL, The Monitor, or British Freeholder, June 3, 1758, at 905, 909.

In 1775, Congress recommended that Connecticut stop sending settlers until further notice.

3 JCC, supra note 3, at 452–53 (Dec. 23, 1775):

Whereas the colony of Connecticut has, by a certain act of their assembly, resolved that no further settlements be made on the lands disputed between them and Pennsylvania, without license from the said assembly, Resolved, That it be recommended to the colony of Connecticut not to introduce any settlers on the disputed lands with Pennsylvania until further order of Congress, or until the dispute shall be settled.

The Constitution did not limit invasions to large-scale incursions—an aspect of the document specifically criticized during the ratification debates.

“John DeWitt,” Letter II, American Herald, Oct. 29, 1787, reprinted in 4 Documentary History, supra note 3, at 156, 160 (arguing “should an insurrection or an invasion, however small, take place, in Georgia” then habeas corpus could be suspended in Massachusetts).

Nor would it seem that “invaders” had to be armed when crossing the border. Even unarmed persons can cause local disruption, and once they cross the border they may acquire arms and defend their position

Thus, there seem to have been no resort to arms when the Connecticut “invasion” crossed the Pennsylvania border. However, the settlers subsequently defended themselves with arms. Sydney George Fisher, The Making of Pennsylvania 237–317 (1896); Mathews, supra note 3, at 68–77.

In Federalist No. 43, Madison justified the broad meaning of “invasion” when discussing the Constitution’s Protection From Invasion Clause: “The latitude of the expression here used, seems to secure each state not only against foreign hostility, but against ambitious or vindictive enterprizes [sic] of its more powerful neighbours.”

The Federalist No. 43, N.Y. Indep. J., Jan. 23, 1788 (James Madison) reprinted in 15 Documentary History, supra note 3, at 439, 442.

There were some limiting factors, however. “Invasion” and its variants did not comprehend all unauthorized intrusions. There had to be detriment (loss, harm, or annoyance) beyond the mere fact of intrusion. Franklin’s letter referred to the “injurious” consequences of the unauthorized immigration into his state.

Supra note 136 and accompanying text.

The actual or threatened detriment from invasion could be injury to persons;

26 id. at 101 (Feb. 26, 1784) (“to defend the persons, liberty and property of the people of the U. S. against an invading and implacable foe”).

Did an incursion have to be organized to qualify as an invasion? We found no evidence that prior coordination was necessary. A spontaneous mob might launch an invasion. On the other hand, prior coordination might demonstrate the existence of detriment or quantify the extent of the risk. Coordination also might demonstrate causation—i.e., that the intrusion was responsible for specified injury.

Relying on the premise that no government in the United States has authority to restrict peaceful immigration, some may exclude non-violent mass immigration from the definition of “invasion.”

E.g., Nikolas Bowie & Norma Rast, The Imaginary Immigration Clause, 120 Mich. L. Rev. 1419 (2022).

Professor Ilya Somin is among the few who deny any federal authority to restrain peaceful immigration from nations with which the United States is not at war. He relies

Ilya Somin, Immigration is Not “Invasion,” Volokh Conspiracy (May 18, 2023, 10:30 AM), https://reason.com/volokh/2023/05/18/immigration-is-not-invasion/.

Nor does the substance of the document provide any evidence on whether Congress has power to restrict immigration.

Madison argued that the Constitution gave Congress no authority to deport “alien friends,” and he classified them as such because they had come from countries with which the United States was at peace.

Madison, Report, supra note 3 (“With respect to aliens, who are not enemies, but members of nations in peace and amity with the United States, the power assumed by the act of Congress, is denied to be constitutional”).

In sum: the modern judicial decisions limiting the term “invasion” only to attacks by an outside sovereignty are clearly erroneous and should not be followed. Rather, as the Constitution employs the words “invasion” and “invaded,” those words denote an unauthorized and uninvited intrusion of any size across a border—including significant unauthorized immigration—where the intrusion causes, or threatens to cause, detriment beyond the fact of the intrusion itself. An invasion need not be armed or even formally organized, although organization does tend to show a link between the intrusion and potential or actual detriment.

Except in cases of actual civil war, official response to insurrection is generally a matter for the police power rather than the war power. Even during civil war, the punishment of insurrectionists is likely to be handled through the civilian criminal justice system, including the prosecution of civil crimes such as treason and sedition.

To the extent permitted by a state constitution, officials may suspend the writ of habeas corpus or declare martial law,

See supra note 112 (remarks of Samuel Adams and Luther Martin). See also Richard L. Aynes, Refined Incorporation and the Fourteenth Amendment, 33 U. Richmond L. Rev. 289, 305–306 (1999) (“The Fourteenth Amendment Founders do not seem to have intended to ‘incorporate’ the Suspension Clause of Article I, Section 9”); cf. Moyer v. Peabody, 212 U.S. 78, 84 (1909) (upholding Colorado statute providing that, “when an invasion of or insurrection in the state is made or threatened, the Governor shall order the national guard to repel or suppress the same”).

Under the Domestic Violence Clause, the state legislature may, by due notice (“Application”) compel the federal government to suppress “domestic Violence.”

U.S. Const. art. IV, § 4, cl. 3.

The Constitution’s Self-Defense Clause specifically recognizes the reserved state power to wage defensive war against invaders.

Id. art I, § 20, cl. 3 (“No State shall, without the Consent of Congress . . . engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.”).

If a state is invaded, the Protection From Invasion Clause requires the federal government to protect that state. However, a state’s ability to respond to the invasion does not depend on federal compliance with the Protection From Invasion Clause. The state may react with the full panoply of measures traditionally associated with defensive war—that is, with all means necessary to repel the invasion,

Supra notes 34 and 36 and accompanying text.

Thus, under the Constitution, a state facing an imminent or actual invasion may issue warnings against further invasion and erect barriers at the border.

Supra note 44 and accompanying text. The barriers must be such as deter invasion while not preventing legitimate passage at a lawful point of entry. See also 2 Vattel supra note 3, at 151 and 153.

Typically, invaders are not in allegiance to the state before the invasion. Rather, they are alien enemies or persons the state lawfully can treat as such. This renders them subject to rules different from those applied to insurrectionists.

Supra notes 172 & 173, and accompanying text.

A decision by federal officials to waive or not enforce applicable federal law may give rise to the claim that the intruder has been “invited” and therefore is not an alien enemy and cannot be treated as such by states. Such a claim might be warranted if that decision is pursuant to state or federal pardon powers; we do not believe such a claim is warranted simply because the executive fails to enforce federal law.

As a practical matter, states and the federal government usually will classify the same people as either alien friends or enemies. However, outside the naturalization and bankruptcy contexts, U.S. Const. art. I, § 8, cl. 4 (“The Congress shall have power… to establish an uniform Rule of naturalization, and uniform laws on the subject of Bankruptcies throughout the United States”), we are aware of no principle requiring uniform classification in all circumstances—particularly if the federal agent has acted contrary to federal law. If uniformity were compelled in the immigration context, no state could deviate from a President’s opinion as to whether the state is invaded—even though the Self-Defense Clause does not involve the President.

In some cases, state policy makers may determine that international criminal organizations qualifying as hostes humani generis comprise all or part of an invasion. In cases of insurrection, a sovereign treats captives as people in allegiance who have abused their trust. In cases of invasion by alien enemies, a sovereign treats them as prisoners of war. But as for “enemies of the human race,” a sovereign may handle them either way.

Supra notes 65 & 66 and accompanying text.

There are clear limits on the power of states to wage defensive war, even when faced with insurrection or invasion. Federal statutes or treaties may override state efforts to restrict immigration or the free flow of goods.

Supra notes 95–100 and accompanying text. But cf. note 260 infra.

More difficult is the question of the extent to which federal execution of incidental powers, such as statutes enacted under the Necessary and Proper Clause,

U.S. Const. art. I, § 8, cl. 18.

There are several relevant Supreme Court cases. Missouri v. Holland

Missouri v. Holland, 252 U.S. 416 (1920).

Bond v. United States

Bond v. United States, 572 U.S. 844 (2014).

Finally, Prinz v. United States

Prinz v. United States, 521 U.S. 898 (1997).

Several Supreme Court cases have determined that the “republican Form” mandate in Article IV, Section 4 is committed to the political branches of the federal government, and, therefore, “republican Form” cases are not justiciable.

Luther v. Borden, 48 U.S. 1 (1849); Pacific States Telephone & Telegraph Co. v. Oregon, 223 U.S. 118 (1912); Baker v. Carr, 369 U.S. 186 (1962); Rucho v. Common Cause, 588 U.S. ___, 139 S. Ct. 2484, 2506 (2019) (dicta).

Detailed examination of modern justiciability issues is beyond the scope of this article. Several observations may, however, assist in framing future discussion.

First: the Supreme Court’s reasons for rendering “republican Form” cases non-justiciable are based on considerations unique to that portion of Article IV, Section 4. These considerations involve matters of definition (“When is a government republican?”) and matters of practicality (“What is the retroactive and prospective legal effect of declaring a government “non-republican?”).

Luther v. Borden, 48 U.S. 1 (1849) (discussing such factors). Cf. Colgrove v. Green, 328 U.S. 549, 553 (1946) (a court decision hypothetically declaring a state government non-republican followed by the state’s failure to erect a complying government would create a vacuum, such that, “The last stage may be worse than the first”).

Second: the courts’ opinions holding “invasion” cases to be non-justiciable also displayed the belief that the constitutional term “invasion” refers only to a military attack from a foreign government.

See cases cited supra note 253.

Third: The consequences from failing to enforce the insurrection and invasion mandates may be far more severe than those arising from failing to enforce the “republican Form” mandate. If Texas or Montana decided to enthrone a king, the Union could continue with all 50 states intact. Failure to protect a state against insurrection or invasion could sever or topple the Union itself.

One is reminded of the neglect of the administration of President James Buchanan in the face of secession.

Fourth: Judicial failure to enforce the federal duty to protect states from insurrection or invasion would convert a clear constitutional requirement into a mere suggestion that federal politicians could ignore at will. This, in turn, would undercut a central reason the Constitution was adopted: to “provide for the common Defence.”

U.S. Const., Preamble (“provide for the common defence”). On the paramount need for a central authority to protect the Union, see the extended discussions in The Federalist Nos. 4 & 5 (John Jay), Nos. 7 & 8 (Alexander Hamilton), No. 45 (James Madison).

Treating insurrection and invasion as non-justiciable has implications beyond the scope of the federal duty to protect. It also has implications for the extent of state war powers. After all, “Insurrection” and “invasion” not only trigger the federal government’s duty under the Protection From Invasion Clause, but also trigger exercise of state war powers. If the terms are too vague for courts to define for federal purposes, then they also are too vague for courts to define for state purposes. If Protection From Invasion Clause cases are held to be non-justiciable because the Constitution commits the decision of whether and how to protect states against invasion to the political branches of the federal government, then the Constitution even more clearly commits (as demonstrated by the Self-Defense Clause) the determination of whether a state has been “Invaded” or in “imminent Danger” to the state government. If redressibility issues impede justiciability in Protection From Invasion Clause cases, then they could also impede justiciability when a state has gone onto a war footing and raised an army.

To be clear: If federal officials are proceeding in good faith to crush an insurrection or repel an invasion, the courts should not second-guess their tactics.

Cf. United States v. Texas, 599 U.S. 670 (2023) (holding that Texas had no standing in a case seeking to have the government make more arrests under an immigration statute).

Like the issue of justiciability, the choice of remedies against recalcitrant officials is best left to another day. We might suggest, however, that where mandamus, declaratory judgments, or injunctions are not practical, monetary damages might well be. Damages could, for example, fund or reimburse state expenses incurred in addressing the problem without federal assistance.