In so far as the Russian Empire and later the USSR were great world powers, possession of Ukraine was absolutely vital to their global status. Without the population and resources of Ukraine Moscow could not even afford to keep subsidizing the Central Asian republics yet alone clients in far a way places like Cuba, Vietnam, and Ethiopia. The USSR was a state that systematically transferred resources from the richer western republics including Ukraine as well as the even richer, but much smaller Baltic States to poorer republics in Central Asia. Not surprisingly just like in Yugoslavia it was the richer republics that wanted to leave the USSR and keep their own resources and the poorer ones that wanted to remain part of the union and continue to receive subsidies. Hence, the western republics that had a net loss of resources due to membership in the USSR were very keen to leave. The eastern ones with a net gain were very reluctant. Estonia, Latvia, and Lithuania were the first states to demand the restoration of their independence. Kazakhstan was dead last in declaring itself independent from the USSR, doing so after the formal dissolution of the union. If Russia is to once again become a major world power rather than merely a regional power then it needs to recover a significant portion of the resources in Ukraine. How much they are aiming for right now is unclear. But, it certainly extends beyond Crimea and includes some of Ukraine's eastern oblasts.