The democratically, legally elected president of Ukraine was forced to flee the capitol because of a protest fomented by the USA and EU using fascists, anti-semites, anarchists and others. While the democratically, legally elected president of Ukraine was outside the capitol, some of the remaining government officials illegally declared the president to no longer be president and undemocratically and illegally appointed a new president.
With Ukraine in turmoil, the intentions of the illegal Ukrainian president unknown, and knowing the USA and EU had fomented the coup with the intent of gaining control over Ukraine, Russia reacted to protect her only warm water port in an area that has been Russian since Catherine the Great and has a population mostly of Russians.
The covert work by the USA and EU was fumbled and things quickly got out of their hands and they were unprepared for the sudden turn of events. Russia, being right next to Ukraine and Ukraine being a vital interest to Russia was closely monitoring the situation and able to react quickly when they deemed necessary.
The response from Obama and various EU leaders was confused, chaotic and inconsistent. Little wonder Russia wasn't moved by this.
Ukraine is of no vital interest to America. If some of the EU nations believe Crimea is so important, why aren't they leading the charge? America has no business involving herself in other peoples wars, especially when such a war would serve no good purpose for America but would stand the chance of greatly harming her.
I don't think the USA and EU wanted, or want, war with Russia. It's their bumbling that has brought us to where we are today. Now the inept leadership of the USA and EU is trying to save face while avoiding war and hoping this will all blow over.
Behind the scenes are various liberal organizations who hate Putin for his anti-homosexual and anti-abortion stances. These groups are attempting to pressure Obama and EU leaders into escalating matters.
War with Russia over Crimea or Ukraine would be a major mistake for America.