On the one hand Putin doesn't acknowledge the newly formed Ukraine government but never the less he puts Russian/pro Russian troops on the ground to secure the Crimea which is illegal, he blocks the port so that Ukraine ships cannot enter or leave along with blocking the use of the airport. Within days the local Crimea autonomous "government" are able to mount an illegal referendum where 95% of the people vote to become part of Russia again. The voting figures are no doubt rigged ( no International observers present) as Ukrainians and tartars, who make up about 35% of the population, were afraid to vote in fear of Russian reprisals. 

Crimea was gifted to Ukraine (at that time an administrative region of the Soviet Union ) by the Soviet leader Kruschew , 

In 1991 , when the Soviet union collapsed , many  subject regions , split away , the Soviet union was powerless , and could not function itself , many Russians beleive the dismantling was done under duress , as they were too weak to stop it .

 All the regions that left , have large ethnic Russian populations

The Demonstrators in Kiev , ousted the Govt (democratically elwcted ) and put themselves in charge , (with no democratic mandate , they were recognised in an hour by the USA and the UK ,  

Russia beleives that the CIA were funding the dissent in Kiev , by paying the demonstrators , and being so quick to recognise a Govvt , whose first act was to ban the Russian language .

 Putin feared that the USA's attempts to subvert the country , were retalaition for his standing up to them , over Syria , they did not get to bomb Damascus , and the chemical weapons have bene ordelry dismantled , as opposed to another decade long occupation , a'la Iraq

 So he upped the stakes , and secured his Naval Base in the Black Sea (leased to Russia till 2014 )

Russia fears that she is being surronded by the country who spends 10 times more on defence per year , than any other country in the world , the country who regulalry invades and occupies another country , to secure its own oil supplies

http://academic.evergreen.edu/g/grossmaz/interventions.html

Crimea is part of Ukraine and therefore part of the treaty singed in 1954 by Ukraine Russia, USA and UK and it is the Ukraine government who should have been asked for a referendum by Crimea, not Russia. 

Putin has behaved like a dictator and an invader.

 Signed in 1994 , saw a population of ethnic Russians cut off from Russia , 

Western Ukraine itself , has bene part of Poland and Austria , and for the last 300 years part of Russia .

The Americans have been goading the Russians , and now the Russians have come out with decisive action , the Americans realise , sending troops to Ukraine , wont be like Kuwait .

 Obama send Drones into Pakistan every night , and has hundred sof thousands of troop in Iraq and Afghan , i dont think he is the dove of peace , just adept at marketing