It could be geographic considerations. The USSR/Warsaw Pact had pretty secure boarders, but that ended when the Soviet Union fell apart. If Putin can get contro

It could be geographic considerations. The USSR/Warsaw Pact had pretty secure boarders, but that ended when the Soviet Union fell apart. If Putin can get control of Ukraine, that would put the Carpathian mountains between him and an invasion from southern Europe. Northern Europe is still wide-open terrain, but if can get control of the Baltics and eastern Poland, he can constrict land invasion routes to the bottleneck between Kaliningrad and Slovakia. Getting control of Kazakhstan (which, not coincidentally, is also suddenly awash with Russian troops) would similarly give him the ability to dominate other formerly Soviet countries and put mountains between Russia and invasion from the south.