The Shanghai massacre of 12 April 1927, the April 12 Purge or the April 12 Incident as it is commonly known in China, was the violent suppression of Chinese Communist Party (CCP) organizations and leftist elements in Shanghai by forces supporting General Chiang Kai-shek and conservative factions in the Kuomintang (Chinese Nationalist Party, or KMT). Following the incident, conservative KMT elements carried out a full-scale purge of Communists in all areas under their control, and violent suppression occurred in Guangzhou and Changsha. The purge led to an open split between left and right wing factions in the KMT, with Chiang Kai-shek establishing himself as the leader of the right wing faction based in Nanjing, in opposition to the original left-wing KMT government based in Wuhan led by Wang Jingwei.

By 15 July 1927, the Wuhan regime had also expelled the Communists in its ranks, effectively ending the First United Front, a working alliance of the KMT and the CCP under the tutelage of Comintern agents. For the remainder of 1927, the CCP launched uprisings to regain power, marking the beginning of the Chinese Civil War. With the failure of the Guangzhou Uprising however, the Communist power was largely diminished, unable to launch another major urban offensive.