During his campaign of terror to eliminate real or imagined opponents of his regime, Mao Zedong set an official killing quota of one per thousand members of the population, although he tolerated up to three per thousand, according to a historian who has published a new assessment of the era. Frank Dikotter, a history professor at the University of Hong Kong, said that between 1947 and 1957, the Communist Party killed some five million civilians. "Violence was not a by-product, it was a quota," said Dikotter (pictured), author of The Tragedy of Liberation: A History of the Chinese Revolution 1945-57 . Villagers were forced to denounce "landlords", mostly ordinary farmers. Some victims were buried alive, or tied up and dismembered. Even some children were killed as "little landlords". Dikotter said Mao wanted people to denounce each other "so they had their hands bloodied in the pact sealed in blood between the party and the people". "To tie everyone's fate to the regime so they are afraid of the return of the old regime. That's revolution. There is no going back." The early communist regime resorted to violence and intimidation to silence the opposition to its rule, he said. Public executions were often staged in stadiums, watched by hundreds. "From that moment, a lot of people had blood on their hands. It's difficult to see how, having gone through three decades of violence, from land reform, to the famine, to the Cultural Revolution, that none of this would have an effect," he said. From the beginning of its rule until 1957, the Communist Party gradually silenced one group after another: the landlords, the entrepreneurs, the intellectuals and the so-called "anti-revolutionaries". By the end of that period, freedoms of speech, press, movement, association, belief and trade had been eliminated, Dikotter said.