Russia is huge enough as it is. What resources does Ukraine have that Russia needs?
Communism is, always has been, and always will be, a geopolitical movement. History has shown that because of its innate flaws, Communism (especially the Putin-style authoritarian kind) cannot exist whilst surrounded by democratic, free countries. Otherwise it will be exposed as a failed system and its leadership's power will be threatened. You either have to A) shut yourself and your people off to the world (North Korea, Cuba), or B) entrench upon any neighboring countries that may expose your violations of freedom and humanity.