The appears to be a thing called the Budapest Memorandum that we signed back in 1994 to get Ukraine to give up its nukes.
http://en.wikipedia.org/...
(1) to respect Ukrainian independence and sovereignty within its existing borders;
(2) to protect Ukraine from outer aggression and not to conduct aggression toward Ukraine;
(3) not to put economic pressure on Ukraine in order to influence her politics;
(4) not to use nuclear arms against Ukraine.
http://www.dailymail.co.uk/...
A treaty signed in 1994 by the US and Britain could pull both countries into a war to protect Ukraine if President Putin's troops cross into the country.
Bill Clinton, John Major, Boris Yeltsin and Leonid Kuchma – the then-rulers of the USA, UK, Russia and Ukraine - agreed to the The Budapest Memorandum as part of the denuclearization of former Soviet republics after the dissolution of the Soviet Union.
Technically it means that if Russia has invaded Ukraine then it would be difficult for the US and Britain to avoid going to war
Anyone ever hear of or remember this?
The relevant text looks like this...
4.The United States of America, the Russian Federation, and the United Kingdom of Great Britain and Northern Ireland, reaffirm their commitment to seek immediate United Nations Security Council action to provide assistance to Ukraine, as a non-nuclear-weapon State Party to the Treaty on the Non-Proliferation of Nuclear Weapons, if Ukraine should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used.
http://en.wikisource.org/...
Not even sure if it was a treaty passed by the Senate, but we seem to have some level of commitment here.