In response to the standoff in Crimea, Estonian President Toomas Hendrik Ilves announced that he would convene the National Defense Council on March 2 to discuss the crisis and called upon the Baltic states to increase their defense spending. "The events in Ukraine show that this struggle is taking place within Europe as well," he said in a speech to the Baltic Defense College last week. "This sends a clear signal to Estonia and the [other] Baltic states: we must invest more in our national defense." Estonia, along with Latvia and Lithuania, joined NATO in 2004.

"The Baltic states have been among the most vocal EU states during this crisis, urging Russia to abandon its military intervention in Ukraine and respect Ukrainian territorial integrity," Erik Brattberg, a senior fellow at the Atlantic Council, told me. "They will watch the events in Ukraine closely to see if the U.S. and NATO will stand up against Russian aggression."

Recent experiences with Russia also fuel Estonia's concerns. The removal of a Soviet-era war statue from the capital city of Tallinn in 2007 led to riots among ethnic Russians (who make up almost a quarter of Estonia's population) and diplomatic outrage from Moscow. Shortly thereafter, a concerted, three-week cyberattack crippled Estonian government agencies, banks, news outlets, and other organizations—a vital blow to what some have called "the most wired country in Europe." Estonian officials blamed the Kremlin for the cyberattacks, a claim Russian officials vociferously denied.

Linas Linkevicius, Lithuania's foreign minister, responded on Saturday by invoking Article 4 of the North Atlantic Treaty, whereby NATO member states consult one another if their territorial integrity or political independence is threatened, for only the fourth time in the alliance's history (Ukraine is not a NATO member).

Lithuania and its Baltic neighbors "are certainly very worried that what is happening to Ukraine today could happen to them tomorrow," Brattberg told me, noting that both Estonia and Latvia have "significant Russian ethnic minorities." Russian President Vladimir Putin asserted on Saturday that Russia retains the right to protect Russian-speaking populations in Crimea and eastern Ukraine. Both the NATO ambassadors and the NATO-Ukraine Commission will meet tomorrow to plan the alliance's response to the unfolding crisis.

Russia has only one remaining ally in the region: Belarus, often referred to as "the last dictatorship in Europe." Ukraine's northern neighbor has mirrored Russian rhetoric about Ukraine by condemning what it described as "radical and unlawful methods of settling domestic disputes" by pro-European Ukrainians. Alexander Lukashenko, the country's autocratic president for the last two decades, quashed a Belorussian protest movement in 2010, during his rigged presidential election, that was similar to Ukraine's. Lukashenko's ability to influence events in Ukraine is nevertheless "slim," according to Brattberg.