But invocations of genocide represent more than just a superficial casus belli. They reflect Moscow’s sincere belief that, in a world dominated by a hostile West, it is the rightful protector of Russian populations throughout the former Soviet republics.

In that worldview, any break from Moscow’s influence within its sphere constitutes an attack on the Russian people as a whole — particularly in Ukraine, which Mr. Putin considers effectively Russian.

Claims of genocide, then, are a way to assert Russia’s sovereignty throughout an ethnic Russian empire that extends well beyond its formal borders — and a right to control that empire with force.