On the night of August 20–21, 1968, Eastern Bloc armies from four Warsaw Pact countries – the Soviet Union, Bulgaria, Poland and Hungary – invaded Czechoslovakia. The invasion comported with the Brezhnev Doctrine, a policy of compelling Eastern Bloc states to subordinate national interests to those of the Bloc as a whole and the exercise of a Soviet right to intervene if an Eastern Bloc country appeared to shift towards capitalism. The invasion was followed by a wave of emigration, including an estimated 70,000 Czechs initially fleeing, with the total eventually reaching 300,000. In April 1969, Dubček was replaced as first secretary by Gustáv Husák, and a period of "normalization" began. Husák reversed Dubček's reforms, purged the party of liberal members, dismissed opponents from public office, reinstated the power of the police authorities, sought to re-centralize the economy and re-instated the disallowance of political commentary in mainstream media and by persons not considered to have "full political trust". The international image of the Soviet Union suffered considerably, especially among Western student movements inspired by the "New Left" and non-Aligned Movement states. Mao Zedong's People's Republic of China, for example, condemned both the Soviets and the Americans as imperialists.