Within the broader scope of the Cultural Revolution, the Inner Mongolia People's Revolutionary Party Incident was a large-scale campaign to eradicate counter-revolutionaries in the Inner Mongolia Autonomous Region. The Incident is infamous for the extremely brutal punishments used; the Incident resulted in hundreds of thousands of casualties.

The Inner Mongolian People's Revolutionary Party (PRP) was established in October 1925 as a branch of the Comintern. (Inner Mongolia is now a part of China; Outer Mongolia is the modern independent state of Mongolia.) After the end of the eight-year Second Sino-Japanese War in 1945, the PRP originally intended to join the government of Outer Mongolia, but the PRP was rejected. Instead, they turned to independence, establishing the Eastern Mongolian People's Autonomous Government. In 1946, Ulanhu, who was ethnically Mongolian, represented the Chinese Communist Party (CCP) Central Committee in negotiating unification of Inner Mongolia's eastern and western halves. After that, the Eastern Mongolian People's Autonomous Government was dissolved; the PRP ceased to exist, with its members placed under the leadership of the Communist Party. Ulanhu became First Secretary of the Inner Mongolia Autonomous Region Party Committee.

However, Ulanhu expressed doubts about the CCP's multi-year campaign of class struggle; at the Seven Thousand Cadres Conference, Ulanhu also criticized the Great Leap Forward; and Ulanhu tried his best to stay away from Liu Shaoqi's socialist education movement. On May 21, 1966, at a meeting of the North China Bureau of the CCP Central Committee, Ulanhu was designated as a "three-anti element": Anti-Party, anti-socialist, and anti-Maoist. He was also charged with the crime of being an "ethnic separatist". Ulanhu was dismissed from all his positions and imprisoned in Beijing. In May of 1967, the Central Committee appointed Teng Haiqing as Acting Commander of the Inner Mongolia Military Region. In November, the Inner Mongolia Autonomous Region Revolutionary Committee (or "Revolutionary Committee" for short) was established. During the Cultural Revolution, the Revolutionary Committee was charged with taking ethnic separatists into custody.

In July 1968, the Revolutionary Committee headed by Teng Haiqing determined that the PRP somehow still secretly existed; the Revolutionary Committee branded this secret PRP the "New Inner Party", a "reactionary organization lurking in Inner Mongolia to engage in ethnic separatism", and viewed Ulanhu as leader of the New Inner Party. Teng immediately launched a massive purge which intended to "dig out" the "poison of Ulanhu" in Inner Mongolia. This drive, called the "Dig and Purge" campaign, persecuted many, using brutal torture to extract confessions.

As the movement deepened, a split emerged between Gao Jinming and Teng Haiqing, the core members of the Revolutionary Committee; both of them were later subjected to criticism sessions. After that, the Purge became more and more cruel. Various tortures were used, such as forcing victims to eat slag; branding with hot irons; pulling teeth with pliers; stabbing the vagina with wooden sticks; pouring hot salt-water into wounds; and more. Nearly no Mongolian cadres on Party committees were spared, and ordinary residents and ethnically Han cadres were also affected. Opinions vary as to the number of casualties caused by the Purge. The general academic opinion, though, is that 20,000 to 30,000 were killed, 120,000 were disabled, and 500,000 were imprisoned.

In April 1969, during the 9th CCP National Congress, Mao Zedong stated his belief that "In implementing the Cleansing the Class Ranks campaign, Inner Mongolia has already magnified the scale." On May 19, 1969, Teng Haiqing and others submitted "Several Opinions on Resolutely Implementing the Central Committee's Current Work Instructions in Inner Mongolia" to the Central Committee. The "Several Opinions" pointed out that serious mistakes had been made in the process of "digging up" PRP members; dealing with the aftermath should include overturning unjust and false convictions. After Mao gave approval on the 22nd, the purging campaign gradually eased. However, at the time, the CCP believed that Teng Haiqing and others had only made a "magnified mistake"; the CCP considered their overall direction to still be correct.

The Inner Mongolia Incident was not rectified until April 1978. the Inner Mongolia Autonomous Region Party Committee submitted a report arguing that there had never been a "New PRP", that the convictions obtained through extorted confessions were unjust, and that the entire incident should be repudiated. The CCP Central Committee agreed with these conclusions. Commander-in-chief Teng Haiqing's criminal liability was never investigated, because the CCP Central Committee considered him to have "made military contributions in the past".

References: Yang Jisheng, "The World Turned Upside Down: A History of the Chinese Cultural Revolution"; Bu Weihua, "History of the People's Republic of China: Smashing the Old World — Turmoil and Catastrophe in the Cultural Revolution (1966-1968)"; Frank Dikötter, "The Cultural Revolution: A People's History, 1962–1976"