Forty-seven years ago, Soviet troops and their Warsaw Pact allies invaded Czechoslovakia to bring an end to that country's brief period of political liberalization, called the Prague Spring. About 500,000 troops were involved in the invasion and occupation, during which 108 Czechoslovaks died and some 500 were wounded. The invasion ended the political and economic reforms led by Alexander Dubcek and reasserted dominant Soviet and Communist authority in Czechoslovakia. It also helped establish the Brezhnev Doctrine, which Moscow said allowed the U.S.S.R. to intervene in any country where a Communist government was under threat. (Photos from the Czech Press Agency archives)