You speak of "U.S. military expansion in eastern Europe." But my observation is that it was the eastern Europeans, (like the Swedes and Finns today) who begged to be let into NATO. The U.S. didn't force any single NATO member to become a member. They all begged to be let in. Nor was there any opposition to their membership by the original NATO members like the UK, France, Germany, Spain, etc. Isn't it possible that Putin's personal ambitions and the authoritarian nature of the Russian regime are responsible for the war?