Prague was a city in the territory of military and political control of the Soviet Union (see Iron Curtain). The largest Stalin Monument was unveiled on Letná hill in 1955 and destroyed in 1962. The 4th Czechoslovak Writers' Congress held in the city in June 1967 took a strong position against the regime. On 31 October 1967 students demonstrated at Strahov. This spurred the new secretary of the Czechoslovak Communist Party, Alexander Dubček, to proclaim a new deal in his city's and country's life, starting the short-lived season of the "socialism with a human face". It was the Prague Spring, which aimed at the renovation of institutions in a democratic way. The other Warsaw Pact member countries, except Romania and Albania, reacted with the invasion of Czechoslovakia and the capital on 21 August 1968 by tanks, suppressing any attempt at reform.