Near Simferopol, Ukraine (CNN) -- In the wake of Russia's invasion of Crimea, the mood here Tuesday was tense, but the streets appeared eerily calm. Ukraine's Crimea region has become the flashpoint in a geopolitical crisis that has embroiled London, Washington, the United Nations and NATO. In the days since they crossed the border into this strategically important peninsula on the Black Sea, Russian forces have surrounded 10 Ukrainian military bases -- 16,000 troops in the past week, according to Ukrainian officials. There has been no fighting -- or loss of life -- but there were ample signs of preparation.