Wrote this to a friend of mine a few days ago:
The short-view answer is that the revolution which overthrew Ukraine’s corrupt, brutal gov’t is a threat to the corrupt, brutal gov’t in Moscow, and they needed to flex their muscles and make things hard for Ukraine as punishment, for fear that another revolution would spring up in Moscow.
The long view is that “Russia” is a fake identity with a fake history. Under both Peter I and Catherine the “Great” they rewrote history to create a single identity for all the people they conquered. They claim Ukraine as the wellspring of their culture, but Moscow as the political capital. Basically, without Ukraine, the whole “Russian” idea plunges into an identity crisis.