30 September Movement

The Thirtieth of September Movement (Indonesian: Gerakan 30 September, abbreviated as G30S, also known by the acronym Gestapu for Gerakan September Tiga Puluh, Thirtieth of September Movement, also unofficially called Gestok, for Gerakan Satu Oktober, or First of October Movement) was a self-proclaimed organization of Indonesian National Armed Forces members. In the early hours of 1 October 1965, they assassinated six Indonesian Army generals in an abortive coup d'état. Later that morning, the organisation declared that it was in control of media and communication outlets and had taken President Sukarno under its protection. By the end of the day, the coup attempt had failed in Jakarta. Meanwhile, in central Java there was an attempt to take control over an army division and several cities. By the time this rebellion was put down, two more senior officers were dead.

In the days and weeks that followed, the army, socio-political, and religious groups blamed the coup attempt on the Communist Party of Indonesia (PKI). Soon a mass purge was underway, which resulted in the imprisonment and deaths of actual or suspected Communist Party members and sympathizers. Under the New Order, the movement was usually referred to as "G30S/PKI" by those wanting to associate it with the PKI, and this term is also sometimes used by the current government.

Investigations and questioning of Suharto's version of the events were long obstructed in Indonesia. While the Central Intelligence Agency (CIA) initially believed that Sukarno orchestrated all of it, several outside sources found inconsistencies and holes in the army claims, notably Benedict Anderson and Ruth McVey who wrote the Cornell Paper that challenged it.