Matthias Rust's landing on Red Square in 1987 seemed like a pebble that started an avalanche. A purge of the Soviet military leadership followed, "Perestroika" continued, and the Soviet Union collapsed in 1990. The Cold War seemed to be over
Kiev gave up its nuclear arsenal after the collapse of the USSR. The USA, the Russian Federation, Great Britain and Ukraine signed the "Budapest Memorandum" in 1994, which included the obligations that the great powers will have towards Ukraine after it gets rid of its bombs, primarily the protection of Ukrainian sovereignty. When Russia annexed Crimea in 2014, Washington announced that the Budapest Memorandum was not actually legally binding.
