Prudent countries (and individuals) who know what their limitations and abilities are and they are not to challenge a more powerful opponent without either the backing of the law or without qualified support from others.
War , however, is a different kettle of fish as we are learning from this Ukrainian war. In war morality/legality is cast aside by brute force and we are seeing that in the Ukraine and Gaza now.
In Real Geopolitics self interest prevails and this war is no different: NATO: Defend its members (the Ukraine is a questionable extension of that but can be justified on speculation "Ukraine today, perhaps a NATO member tomorrow") USA: To economically weaken Russia so that it can't afford to maintain its Nuke Arsenal and . the means to deliver it). US role in this war also counterbalances China's economic . influence in Europe , particularly in Germany.
Monroe Doctrine: To keep out European Powers out of the Americas.
Perhaps Europe needs and equivalent: To Keep out US Power out of Europe ? .
