After the Russian Revolution, sociology was gradually "politicized, Bolshevisized and eventually, Stalinized". From 1930s to 1950s, the discipline virtually ceased to exist in the Soviet Union. Even in the era where it was allowed to be practiced, and not replaced by Marxist philosophy, it was always dominated by Marxist thought; hence sociology in the Soviet Union and the entire Eastern Bloc represented, to a significant extent, only one branch of sociology: Marxist sociology. With the death of Joseph Stalin and the 20th Party Congress in 1956, restrictions on sociological research were somewhat eased, and finally, after the 23rd Party Congress in 1966, sociology in Soviet Union was once again officially recognized as an acceptable branch of science.