President Obama has decided to get tough with Russia by imposing sanctions and increasing support for Ukraine’s new government. This is a big mistake. This response is based on the same faulty logic that helped precipitate the crisis. Instead of resolving the dispute, it will lead to more trouble.

The White House view, widely shared by Beltway insiders, is that the United States bears no responsibility for causing the current crisis. In their eyes, it’s all President Vladimir V. Putin’s fault — and his motives are illegitimate. This is wrong. Washington played a key role in precipitating this dangerous situation, and Mr. Putin’s behavior is motivated by the same geopolitical considerations that influence all great powers, including the United States.

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. The Russians have intensely disliked but tolerated substantial NATO expansion, including the accession of Poland and the Baltic countries. But when NATO announced in 2008 that Georgia and Ukraine “will become members of NATO,” Russia drew a line in the sand. Georgia and Ukraine are not just states in Russia’s neighborhood; they are on its doorstep. Indeed, Russia’s forceful response in its August 2008 war with Georgia was driven in large part by Moscow’s desire to prevent Georgia from joining NATO and integrating into the West.

Fast forward to last November, when it seemed that President Viktor F. Yanukovych would sign an agreement with the European Union that was designed to deepen Ukraine’s integration with the West and greatly reduce Moscow’s influence there. Mr. Putin offered Ukraine a better deal in response, which Mr. Yanukovych accepted. That decision led to protests in western Ukraine, where there is strong pro-Western sentiment and much hostility to Moscow.