The US started it by spending an obscene amount of money fomenting regime change.
This administration did the same thing in Egypt, Libya, Syria, and throughout the Arab Spring. If they can destabilize Ukraine and have their way there, they've completely surrounding Russians border. Ukraine is the biggy....
What they don't get is Russia is not going to give up influence in Ukraine under any circumstances.
The U.S. sent 5 billion over twenty years, including during Yanukovich's election, a clear Russian puppet, and other leaders besides. The U.S. spends money like that on a huge amount of developing countries. The regime change was accomplished through the Jewish, Russian, Ukrainian, and other dissidents and the Ukrainian parliament's actions.
FYI, if Yanukovich hadn't of been having people kidnapped and beaten by his hired goons even BEFORE the Maidan protests, he might have still been in power today. The shooting that came later was only the climax of the dictator's actions. A course of action, by the way, recommended by the Russian GRU.