This doctrine was announced to retroactively justify the invasion of Czechoslovakia in August 1968 that ended the Prague Spring, along with earlier Soviet military interventions, such as the invasion of Hungary in 1956. These interventions were meant to put an end to liberalization efforts and uprisings that had the potential to compromise Soviet hegemony inside the Eastern Bloc, which was considered by the Soviet Union to be an essential and defensive and strategic buffer in case hostilities with NATO were to break out.