Actually, the answer as to why this all happened is quite nuanced. No, the new Ukraine government is not a US puppet.
1) Viktor Yanukovych attempted to bring Ukraine under Russian influence. The people in Western Ukraine naturally revolted, as they want to be part of the Western alliance.
2) Crimea has a majority Russian population. They support Russia, and welcomed the Russian invasion.
3) This is a situation where you had 2 different ethnicities living under one roof, which was an unstable situation that could not last.
4) Viktor Yanukovych and his henchmen were Oligarchs who looted the treasury and turned it into their private piggy bank. The new leadership in Ukraine consists of Oligarchs who are looting the treasury, and turning it into their private piggy banks. Some things just don't change, despite change.
How the hell can people claim that the CIA was behind this? There is absolutely no evidence to support that. The facts point to the obvious reason. Western Ukranians, and Crimean Russians could never stand each other. Something had to give.
Dead on. That area of the world, has been dealing with ethnic unrest since the Roman's left... well, actually, long before that. In other words, this isn't new. They've caused many wars, including WWI directly, and it could be argued, WWII.
There's not that much difference between the ethnic unrest in this region and the tribal sectarian unrest in the ME. Ancient hatred that has never been quelled.
The closest thing we can compare it to in the US is racial tensions. But the racial tensions in the US are in no way truly comparable to the violent hatred and aggressive discrimination between the different ethnicities in that region of the world. And because of that, very, very few many Americans can actually understand the real interactions and reasons behind the hostilities being played out right now.
And even less Americans understand IR; case in point the multitude of posts regarding State Department phone calls, and God knows what else they use to blame this on the US.
Russia is acting Russia's best interest. Ukraine's new government is acting in Ukraine's best interest and the US is acting in the US' best interest. As are all other nations involved in this. That's also why China is not voting on the resolutions in the UN; it's in China's best interest to stay neutral at this time. That interest? It's financial.
It all comes down to money. Money that flows from petroleum (natural gas and oil) as well as territorial dominance (the port at Sevastopol which is a warm water port). The ethnic unrest is a tool used by all involved to forward their financial agenda.
Unlike what some here have stated, it IS NOT the corporations. It's larger than that. It's the countries themselves that want the money and the leaders of those countries that want their share. Some of that may come from corporations that would profit from dominance in the area, but in the case of many of the players, it's not the corporations themselves, since the countries and their leaders are the owners. In some instances, like the US, it's tax dollars, loan proceeds and trade income as well as the IR goal of putting Putin and the Russians in a box and keeping them there.
If the US can keep Putin in that box, the US can maintain their role as the dominant source of financial assistance in the world. This is used by the US as IR leverage to get our way.
There are many, many other reasons also, but the tin foil hat conspiracy theories being batted around are not even close to the mark.