Russia is using military force in Crimea to attempt separating Crimea from the Ukraine.
This action is in direct violation of Budapest Memorandum on Security Assurances may be summarized as follows: Russia, the UK and the USA undertake to respect Ukraine's borders in accordance with the principles of the 1975 CSCE Final Act, to abstain from the use or threat of force against Ukraine, to support Ukraine where an attempt is made to place pressure on it by economic coercion, and to bring any incident of aggression by a nuclear power before the UN Security Council. Ukraine voluntarily has destroyed all the nuclear weapons on its territory, including strategic offensive weapons as part of security assurances by Russia, the UK and the USA. USA has to stop these violations.