Russian aggression against Ukraine and the law of countermeasures – a momentum for caution or an opportunity for evolution?

The paper addresses some of the challenging legal issues invoked by the response of the part of the international community to the Russian aggression in Ukraine in 2022. These legal issues were selected through the lenses of evolution versus caution paradigm. In particular, it maps the issue of the permissibility of third--party countermeasures, a topic that has already enjoyed attention of the doctrine but is still controversial. It then focuses on the issue of confiscation of frozen Russian assets as a possible form of countermeasure. This issue is addressed through the optics of the human right to private property and briefly also through the lenses of the law on the immunities of States. The paper then addresses a complicated issue of possible claims against sanctions initiated in international investment arbitration. It focuses primarily on the question whether host States can raise the defence of countermeasures in investment arbitration.