As Mearsheimer writes:
Putin’s actions should be easy to comprehend. A huge expanse of flat land that Napoleonic France, imperial Germany, and Nazi Germany all crossed to strike at Russia itself, Ukraine serves as a buffer state of enormous strategic importance to Russia. No Russian leader would tolerate a military alliance that was Moscow’s mortal enemy until recently moving into Ukraine. Nor would any Russian leader stand idly by while the West helped install a government there that was determined to integrate Ukraine into the West.
Washington may not like Moscow’s position, but it should understand the logic behind it. This is Geopolitics 101: great powers are always sensitive to potential threats near their home territory. After all, the United States does not tolerate distant great powers deploying military forces anywhere in the Western Hemisphere, much less on its borders. Imagine the outrage in Washington if China built an impressive military alliance and tried to include Canada and Mexico in it. Logic aside, Russian leaders have told their Western counterparts on many occasions that they consider NATO expansion into Georgia and Ukraine unacceptable, along with any effort to turn those countries against Russia -- a message that the 2008 Russian-Georgian war also made crystal clear.
The core problem according to Mearsheimer is that both sides are operating under different paradigms, Russia is realist realpolitik while the West is liberal and idealistic. His solution is:
There is a solution to the crisis in Ukraine, however -- although it would require the West to think about the country in a fundamentally new way. The United States and its allies should abandon their plan to westernize Ukraine and instead aim to make it a neutral buffer between NATO and Russia, akin to Austria’s position during the Cold War. Western leaders should acknowledge that Ukraine matters so much to Putin that they cannot support an anti-Russian regime there. This would not mean that a future Ukrainian government would have to be pro-Russian or anti-NATO. On the contrary, the goal should be a sovereign Ukraine that falls in neither the Russian nor the Western camp.
To achieve this end, the United States and its allies should publicly rule out NATO’s expansion into both Georgia and Ukraine. The West should also help fashion an economic rescue plan for Ukraine funded jointly by the EU, the International Monetary Fund, Russia, and the United States -- a proposal that Moscow should welcome, given its interest in having a prosperous and stable Ukraine on its western flank. And the West should considerably limit its social-engineering efforts inside Ukraine. It is time to put an end to Western support for another Orange Revolution. Nevertheless, U.S. and European leaders should encourage Ukraine to respect minority rights, especially the language rights of its Russian speakers.
Let's hope saner and cooler heads prevail in this escalating conflict.