The reform movement was viewed by Leonid Brezhnev and other Soviet hard-liners in Moscow as a serious threat to the Soviet Union's hold on the Socialist satellite states, they decided to act. In the first hours on the 21st August 1968 Soviet planes began to land unexpectedly at Prague's Ruzyne airport, and shortly Soviet tanks would roll through Prague's narrow streets. Within hours foreign troops would take up strategic positions throughout the city, including surrounding the building of the Central Committee of the Communist Party, taking hold of Wenceslas Square, and eventually taking over Czechoslovak radio and television. Around 500,000 troops invaded and occupied Czechoslovakia in an operation code-named "Danube."
Some 500 Czechoslovaks were wounded and 108 killed in the invasion, which successfully ended political and economic reforms under the leadership of Alexander Dubcek and gave the Communist Party greater authority. The Soviet-led invasion 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. The Soviet backed occupation of Czechoslovakia would last until the velvet revolution brought an end to the Communist dictatorship in November 1991 as the Cold War ended.