The US has no business in their civil war. It would be the same thing as Russia siding with the Confederacy in the US civil war and then looting all of the North's resources after a Southern victory.
The US CIA incited the overthrow of the Ukrainian government. The new Ukrainian government immediately doled out ownership and development of coal and gas resources in the east including Crimea to US corporations in repayment for US support even though the fascist government of Kiev didn't own said resources. They cut pensions, raised taxes, deeply indebted the country with loans from the IMF, bailed out banks, etc. They also began working toward inducting Ukraine into NATO which the people of east Ukraine vehemently oppose. The people of east Ukraine revolted because the new government didn't represent them. Putin seized Crimea (which used to be part of Russia anyway) to protect the Russians that live there, they took a vote a huge majority of the population wanted to join Russia. If the US minded its own business the Russians would have never taken Crimea.
US state dept. caught on tape discussing who will run the new government and who will be thrown out before the CIA supported coup: http://www.youtube.com/watch?v=NTos0duooaU
Crimea is better off with Russia than the US, at least Russian owned Gazprom offered the Ukrainian owners partnership in resource development unlike the US that wanted to dominate everything. The majority of citizens who live in Crimea democratically voted to become a part of Russia. Russia raised pensions instead of cutting them.
The main thing that elevates tensions between the US and Russia is NATO bases and weapon systems enclosing Russia in (building another Iron Curtain around Russia as Putin would say). They've said this many times which is why they seriously object to the US inducting Ukraine into NATO and so do half of Ukrainians. The US aided in the overthrow in order to make Ukraine a NATO country. Putin's reaction shouldn't be a surprise to anyone. The US government just doesn't like Russia because Putin calls them out on their bullshit and the US politicians are extremely jealous of Putin's 85% approval rating.
And it was the US backing Kiev when they shot down MH17 to incite hatred toward Russia. http://www.storyleak.com/evidence-conclusive-ukraine-military-shot-down-mh17-in-false-flag-operation/
http://www.wsws.org/en/articles/2014/08/09/mala-a09.html A Thursday article in the New Straits Times, Malaysia’s flagship English-language newspaper, charged the US- and European-backed Ukrainian regime in Kiev with shooting down Malaysian Airlines flight MH 17 in east Ukraine last month. Given the tightly controlled character of the Malaysian media, it appears that the accusation that Kiev shot down MH17 has the imprimatur of the Malaysian state.
The New Straits Times article, titled “US analysts conclude MH17 downed by aircraft,” lays out evidence that Ukrainian fighter aircraft attacked the jetliner with first a missile, then with bursts of 30-millimeter machine gun fire from both sides of MH17. The Russian army has already presented detailed radar and satellite data showing a Ukrainian Sukhoi-25 fighter jet tailing MH17 shortly before the jetliner crashed. The Kiev regime denied that its fighters were airborne in the area, however.
The US propaganda media's story doesn't even make sense: How would shooting down a foreign plane that isn't hostile have any benefit to Russia whatsoever? Did anyone see the way Russia took Crimea?- very careful not to cause civilian casualties because they knew they would take a lot of criticism regardless. If anything US foreign policy has been much more aggressive than Russian. Malaysia Airlines is also suing the government in Kiev for the incident, not the Russians. There are satellite pictures of the Ukrainian fighter and no evidence of Russian involvement other than the wild accusations made by the media. Did you notice how the media hasn't offered any follow up on this topic? It's because their propaganda has been exposed and now they're just trying to keep it contained.
Putin also wrote a letter to the US citizens urging them to not support Obama's plans to topple the Syrian government based on allegations of chemical weapons use which we later found out was Al Qaida and not the Syrian government. http://www.nytimes.com/2013/09/12/opinion/putin-plea-for-caution-from-russia-on-syria.html
East Ukraine separatists seek union with Russia- BBC
Overwhelming Support for Breakaway in Crimea Raises East-West Tensions; U.S. Prepares Sanctions-WSJ
Ukraine's Donetsk region asking to join Russia- CNN
Donetsk region asks to join Russia- The Guardian
Request comes just two hours after referendum results show 90% voted for independence from Ukraine
......
http://www.reuters.com/article/2014/03/13/us-ukraine-crisis-un-idUSBREA2C2DE20140313
Russia vows to veto U.S. draft at U.N. declaring Crimea vote illegal
UNITED NATIONS Thu Mar 13, 2014 7:01pm EDT
(Reuters) - The United States circulated a draft resolution to the U.N. Security Council on Thursday that would declare Sunday's planned referendum on independence for Ukraine's Crimea region illegal, but Russia has vowed to veto it, council diplomats said.
Diplomats said the one-page resolution would urge countries not to recognize the results of the vote in pro-Russian Crimea, whose parliament has already voted to join Russia.
Notorious Anti-Putin Journalist goes on Ukrainian TV and tells the real situation in the East but the Ukrainians try to shut him up: https://www.youtube.com/watch?v=VSEkcCavcmE