The Yan'an Rectification Movement was a political mass movement led by the Chinese Communist Party (CCP) from 1942 to 1945. The movement took place in the Yan'an Soviet, a revolutionary base area centered on the remote city of Yan'an. Although it was during the Second Sino-Japanese War, the Chinese Communist Party was experiencing a time of relative peace when they could focus on internal affairs. The legacies of the Yan'an Rectification Movement proved fundamental to the subsequent history of the Chinese Communist Party, according to Kenneth Lieberthal. These included the consolidation of Mao Zedong's paramount role within the Chinese Communist Party, especially from 1942 to 1944, and the adoption of a party constitution that endorsed Marxist-Leninism and Mao Zedong Thought as guiding ideologies. This move formalised Mao's deviation from the Moscow party line and the importance of Mao's alleged 'adaptation of communism to the conditions of China'. The Rectification Campaign was successful in either convincing or coercing the other leaders of the Chinese Communist Party to support Mao. Because the Chinese Communist Party had overcome great odds to grow and develop during this period, the methods employed in Yan'an were looked upon in reverence during Mao's later years. After the founding of the People's Republic of China in 1949, Mao repeatedly used some of the tactics that had been successful in Yan'an whenever he felt the need to monopolize political power. To a large extent, the Yan'an Rectification Campaign began with the "systematic remolding of human minds." The United States Joint Publications Research Service estimated that more than 10,000 were killed in the "rectification" process, as the Chinese Communist Party made efforts to attack intellectuals and replace the culture of theMay Fourth Movement with that of Chinese Communist Party culture. The rectification movement is regarded by many as the origin of Mao Zedong's cult of personality.