In 1994, the US, Russia & the UK signed a document - the Budapest Memorandum. They committed "to respect the independence and sovereignty and the existing borders of Ukraine" & "to refrain from the threat or use of force" against the country. Those assurances, were key in persuading the government of Ukraine to give up what amounted to the world's then third largest nuclear arsenal, consisting of some 1,900 strategic nuclear warheads. Kyiv did nothing provocative to warrant the invasion other than want to be free.