After the U.S./EU/NATO supported coup in Kiev Russia took steps to secure its vital seaport at Sevastopol on the Crimea. With their plans to use Sevastopol for themselves and to thereby blockade Russia from influence in the Mediterranean stopped by the Russian move various reactionaries immediately demand an expansion of NATO to somehow stop further "Russian aggression":
[T]he US should work with its allies in NATO to build consensus for an immediate announcement by the alliance that NATO membership will be extended to Montenegro and Macedonia and make the commitment to a Membership Action Plan for Georgia at the NATO summit in Cardiff.
These people invert cause and effect. Russia reacted like it did because of NATO's expansion since the late 1990. Such a reaction was utterly foreseeable and was foreseen when the very first NATO expansion towards the East happened.
George Kennan was the U.S. diplomat and Russia specialist who developed the cold war strategy of containment of the Soviet Union, though he later criticized its militaristic implementation. In 1998, when the Senate voted to extend NATO to include Poland, Hungary and the Czech Republic, Kennan was asked to comment. He responded:
"I think it is the beginning of a new cold war," said Mr. Kennan from his Princeton home. "I think the Russians will gradually react quite adversely and it will affect their policies. I think it is a tragic mistake. There was no reason for this whatsoever."
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"It shows so little understanding of Russian history and Soviet history. Of course there is going to be a bad reaction from Russia, and then [the NATO expanders] will say that we always told you that is how the Russians are — but this is just wrong."
NATO expansion and the putsch in Kiev are, as Kennan predicted, the reason that Russia acts as decisive as it does. A harsh Russian reaction because of NATO extension is NOT a good reason to extend NATO further. The Russian (and Chinese) reaction to that would likely be even harsher. No one serious should wish back the times when nuclear war often looked imminent. Luckily neither the public in the U.S. nor in the EU is willing to go that way.