We're actually talking about your assertion that Russia's expansion has always been defensive in nature and an effort to establish a "buffer zone". The U.S. and its potential empire are irrelevant to that claim.
Their primary motivation has been defensive, yes, but if you want to look at each and every event and find situations where they were the aggressor, you can certainly find them. I wasn't denying any historical facts about what they've done, but just addressing the underlying perception which motivates such a posture.
You admit here that it's wrong to invade other countries and try to take them over. Before you said you offered no moral judgement on Russia invading and taking over other countries. So, at least we've resolved that.
Well, it's good that we've resolved something, but I don't really see it in the same way. When it comes to moral questions, it's kind of like the "lesser of two evils," where one might still need to take a morally wrong choice if all the other choices lead to a worse outcome. This can get even more dicey because we don't know and can't predict all the possible outcomes.
Russia has not expanded for defensive reasons. They haven't sought to create a "buffer zone". They have expanded the same way every other country/land/nation/state/etc. has ever expanded, through conquest meant to increase their power and land.
Russia has plenty of land already. They are the largest country in the world by area. They don't need any more land.