Commentators who try to explain Russia’s invasion of the Crimea are right to point out the former superpower’s many grievances. But those should be not mistaken for a justification of its actions.

Russia moved troops into the Crimean Peninsula, which headquarters its Black Sea Fleet, late last month, when the country’s relatively pro-Russian president, Viktor Yanukovich, was deposed after months of protests against his decision to pull out of an associated agreement with the European Union in favor of deeper ties with Russia.

The move — which Western leaders have rightly condemned as a breach of Ukrainian sovereignty and Russia’s own treaty obligation to it — follows two decades of perceived Russian humiliation by the West. As Russia saw it, Ukraine was but the latest of former satellite states the West tried to snatch from under its nose.

Writing in The New York Times , John Mearsheimer, a political scientist, explains, “The taproot of the current crisis is NATO expansion and Washington’s commitment to move Ukraine out of Moscow’s orbit and integrate it into the West.” Whereas Russia — grudgingly — tolerated NATO’s expansion into its former Soviet sphere after the end of the Cold War in 1991, he believes it drew a line in the sand when the alliance considered admitting Georgia and Ukraine in 2008.

Drawing on Mearsheimer’s analysis, Tom Switzer, who is a research associate at the United States Studies Center at the University of Sydney, argues that the West “provoked” Russia by leaving open the possibility of Georgia and Ukraine joining NATO and that its response to alleged Western meddling in Ukraine is both rational and “understandable.”

Pat Buchanan, a former Republican Party presidential candidate and conservative commentator, is even more sympathetic to Russia’s motives. He predicts at his blog that future historians “will as surely point to the Bushes and Clintons who shoved NATO into Moscow’s face” if there is to be a second Cold War. (The first NATO expansion following the Soviet Union’s collapse came with Germany’s reunification when George H.W. Bush was president; the second under Bill Clinton; the third under George W. Bush.)

What the West should do, according to Mearsheimer, is not oppose Russia’s blatant invasion of a neighboring country, and what appears an attempt to annex part of it, but “emphasize that Georgia and Ukraine will not become NATO members. It should make clear that America will not interfere in future Ukrainian elections or be sympathetic to a virulently anti-Russian government in Kiev.”

There is truth in what Buchanan, Mearsheimer, Switzer and others — including Stephen F. Cohen writing in The Nation , The New York Times ‘s Thomas Friedman and the Daily Mail ‘s Peter Hitchens — have argued. Russia does mistrust the West’s motives and sees the gradual eastward expansion of the European Union and NATO as a threat to its security. But this does not justify Russia’s behavior.

For one thing, Cathy Young writes in Time magazine, the West also made efforts to comfort Russia. It provided $55 billion in aid for its economic reconstruction between 1992 and 1997 alone. Russia was invited to the club of top industrialized nations, which became the G8. It was included in NATO’s Partnership for Peace program and a NATO-Russia Council was founded in 2002 to facilitate security cooperation.

NATO did expand but so what? If Russia ever expected an attack from the West once the Cold War had ended, this was surely paranoia. Russia’s “humiliation” had far more to do with its own misguided experiment in communism than the liberation of Central and Eastern European nations from communism’s embrace.

Sadly, this paranoia is real and many, if not most, Russians have yet to come to terms with their loss of empire, evidenced in their continued admiration for tyrannical leaders from the past and willingness to believe that whatever ails their country is the result of foreign plots.

Western leaders would be wise to take this, far from rational, Russian mindset into account when dealing with the country. But that is not to say they should attempt appeasement.

Lilia Shevtsova, a senior fellow at the Carnegie Moscow Center, argues in The American Interest against letting Vladimir Putin get away with annexing the Crimea. Western inaction in Ukraine would follow Western inaction in 2008 when Russia virtually annexed Georgia’s breakaway regions of Abkhazia and South Ossetia — which, like the Crimea, are home to ethnic Russian majorities — and not only validate the recreation of a Russian sphere of influence but the reintroduced of a “doctrine of interference” under the pretext of protecting Russian compatriots. She warns, “Since Russian speakers live in most of the newly independent states, this ‘doctrine’ threatens the stability of the entire post-Soviet space.”

Whatever Russia’s grievances, real or imagined, they are no justification for a return to an international order in which big states invade and carve up smaller ones simply because they can. In this sense, American secretary of state John Kerry’s exasperation — “You just don’t in the twenty-first century behave in nineteenth century fashion by invading another country on completely trumped up pretext,” he said on CBS News’ Face the Nation last week — was perfectly appropriate.

Now the United States and its allies just need to come up with a more powerful response.