Michael Rubin, a former Pentagon official now at the American Enterprise Institute think tank, said Putin was also motivated by domestic considerations and his standing had been boosted by his response to the Ukrainian crisis.
"Putin's economic stewardship hasn't been good," Rubin said. "There's been great stagnation in Russia. What Putin has discovered, first with Georgia and now with the Crimea, is that you can distract the Russian public."
One of Obama's early acts on taking office was to cancel an anti-ballistic missile shield due to be based in Poland and the Czech Republic. Radek Sikorski, Poland's foreign minister, was so incensed by what he viewed as a betrayal that he refused to take a telephone call from the White House.
Not only did the former Soviet satellites feel abandoned by the Americans, but Putin took note that as Obama tried to extricate the US from the Middle East and "pivot" to the Pacific, he treated eastern Europe as a strategic backwater.
Rubin said Putin was unlikely to stop at Crimea and would probably seize more Ukrainian territory before focusing on the Baltic states. I don't think the US and NATO will do much of anything," he said. "Ultimately, I don't think the West has the stomach for this."
In an article circulated widely in Washington, Anders Aslund, a former economic adviser to Russia and Ukraine, wrote that Putin's address had created an "awful sense of deja vu" because it was reminiscent of Hitler's declaration of war on Poland in 1939.
"Europe is in poor shape militarily, unprepared to stand up against Russia after two decades of disarmament. Once again, the situation is reminiscent of Europe in 1938. Russia's military might not be in great shape either, but Russia is the only European country that has pursued serious military reform and rearmament."