The key moment in escalating Sino-Soviet tensions was the Soviet invasion of Czechoslovakia on 20–21 August 1968 and the proclamation of the Brezhnev Doctrine that the Soviets had the right to overthrow any communist government that was diverging from what defined by the Kremlin. Mao saw the Brezhnev doctrine as the ideological justification for a Soviet invasion of China to overthrow him and launched a massive propaganda campaign attacking the invasion of Czechoslovakia although he had condemned the Prague Spring as "revisionism". On 21 August 1968, the Romanian leader Nicolae Ceaușescu gave a famous speech in Revolution Square in Bucharest that denounced the invasion of Czechoslovakia. It was widely seen both in Romania and abroad as virtual declaration of independence from the Soviet Union. Romania started to move away from being in the Soviet sphere of influence to the Chinese sphere of influence.