In 1968, following the Prague Spring, the country was invaded by the Warsaw Pact forces (People's Republic of Bulgaria, People's Republic of Hungary, People's Republic of Poland, and Soviet Union, with the exception of Socialist Republic of Romania and People's Socialist Republic of Albania) in 1968, ending a period of liberalisation under the leadership of Alexander Dubček. 137 Czechoslovak civilians were killed and 500 seriously wounded during the occupation.