The theory of aggravation of the class struggle along with the development of socialism was one of the cornerstones of Stalinism in the internal politics of the Soviet Union. It was put forward by Joseph Stalin in 1933 and supplied a theoretical base for the claim that ongoing repression of political opponents is necessary.
Stalin argued that the further the country would move forward, the more acute forms of struggle will be used by the doomed remnants of exploiter classes in their last desperate efforts - and therefore, political repression was necessary to prevent them from succeeding in their presumed goal of destroying the Soviet Union. Stalin believed that the class enemy could even worm its way into the party claiming to lead a socialist state. He evaluated his associates of the day based on whether they acted on that belief or the belief that a party could have no enemies inside it. Tolerance inside the Party to those who disagreed with the official Party line was called by Stalin "rotten liberalism". He believed such tolerance would make the Party weak and eventually lead to its destruction. As a result, he argued that purges were sometimes necessary.
The notion of the aggravation of class struggle stands in contrast to the ideas of other communists, such as Nikolai Bukharin or Leon Trotsky, who argued that there was no longer any bourgeoisie in the Soviet Union to have to struggle with.
Mao Zedong developed Stalin's idea further, saying that there is the possibility of an entire bourgeoisie developing inside the Communist Party leading a socialist state before the establishment of communism. Mao stressed the supposedly domestic roots of that bourgeoisie, while Stalin focused more on presumed Western spies. According to Mao, the bourgeoisie inside the party aimed at the restoration of capitalism. Mao also held that "peaceful evolution" was the goal of the foreign capitalists, and that the restoration of capitalism could happen from within, without war, if there were an ebb in the class struggle.
Upon the death of Mao, Deng Xiaoping rejected Mao's theory of the "bourgeoisie in the party" and as a result opened the doors to the restoration of capitalism in China.