Russia’s invasion of Ukraine is an illegal war of aggression.
In 1923, just five years after the end of the First World War, the US Secretary of State Charles Evans Hughes, who would subsequently serve as Chief Justice, stated that “war should be made a crime, and those who instigate it should be punished as criminals.”
International humanitarian law developed when there was no international prohibition on the right to wage war. Since the adoption of the UN Charter in 1945, there is a general prohibition on the use of force by states except in accordance with the provisions of the Charter. The legality of the resort to armed conflict by states is, therefore, a question of international law, while the conduct of those engaged in hostilities is governed by international humanitarian law. Individuals violating international law governing the use of force may be charged with the crime of aggression or crimes against peace, while those violating humanitarian law may be prosecuted for war crimes. In this way, international humanitarian law applies to all parties, i.e. to those lawfully resorting to the use of force as well as to those deemed to be acting unlawfully.
The invasion of Ukraine by Russia is a violation of the UN Charter, which under Article 2(4), prohibits the “threat or use of force against the territorial integrity or political independence of any state.” There were no grounds to support the claim by Russia of self-defence. Indeed, all of Putin’s claims have been thoroughly refuted as pretexts for the invasion, which constitutes an act of aggression and is contrary to international law. Putin, as president, may also be individually responsible for the crime of aggression, one of the core crimes set out in the Rome Statute of the International Criminal Court. However, there are significant legal hurdles to be overcome before this would be possible as Russia is not a party to the International Criminal Court statute.