A little footnote from "simplythebeast's" link
Russia, along with the US, UK and France, pledged to uphold the territorial integrity of Ukraine in a memorandum signed in 1994.
Another data point supporting my old notion that Warren Christopher was in a job that was way over his head. If you look at a map and think through what that guarantee means .. it's like the French guaranteeing Poland's territorial integrity in about 1936.