 Albania, which had become increasingly isolated under Stalinist leader Enver Hoxha following de-Stalinization, undergoing a Soviet–Albanian split in 1961, withdrew from the Warsaw Pact in 1968 following the Warsaw Pact invasion of Czechoslovakia.In 1917, Russia restricted emigration by instituting passport controls and forbidding the exit of belligerent nationals.In 1922, after the Treaty on the Creation of the USSR, both the Ukrainian SSR and the Russian SFSR issued general rules for travel that foreclosed virtually all departures, making legal emigration impossible.