The government's attitude to Jews and Zionism shifted after 1948, leading to the 1952 Slánský trial in which the Czechoslovak government accused fourteen Communists (eleven of them Jewish) of belonging to a Zionist conspiracy. Political censorship hampered the study of the Holocaust, and memorials to the victims of fascism did not mention Jews. In the 1960s, which were characterized by a liberalization known as the Prague Spring, discussion of the Holocaust opened up. The Academy Award-winning 1965 film, "The Shop on Main Street", focused on Slovak culpability for the Holocaust. Following the 1968 Warsaw Pact invasion of Czechoslovakia, authorities cracked down on free expression,