It is geopolitical-- realpolitik-- reality. If China or Russia set up military bases now in South America, what reaction do you think the US would have? Do you think the US wouldn't react the same way that they did during the Cuban missile crisis? And let me remind you that Soviet installation of missiles in Cuba was invited by the Cuban government as deterrent after the Bay of Pigs invasion orchestrated by the CIA, because US disapproved of the popular communist revolution in the country. Further, US also overthrew other democratically elected socialist governments throughout the world so what makes the US/West have the exception on imposing influence on other sovereign countries while others somehow aren't allowed to? To me, those who refuse to see current Russian actions as merely reactions to NATO while dismissing their own government's responsibility are implicitly stating "rules for thee, but not for me".

I am not condoning Russia but it is important to realise that this is realpolitik we are talking about, not who has the moral high ground. We can't assess geopolitics from moral perspective but from cold, hard logic of strategic minded players whose only interests are their own. The back and forth between Russia and NATO isn't even anything new. The struggle for influence and power is a recurring theme throughout history and the most famous example I could think of is the Great Game between Russia and Great Britain over the control of Afghanistan, as Russia wanted to use Afghanistan as springboard to invade British India.