Between October 1965 and March 1966, members and supporters of Indonesia’s Communist Party, or PKI, the third largest in the world at the time, were hunted down and murdered. Historian Robert Cribb estimates 200,000 to 800,000 people were killed.

The anti-communist violence brought Suharto to power in 1967, replacing the country’s founding president Sukarno. In the midst of the Cold War, the tragedy changed Indonesia from a fiercely independent Asian nation into a pro-Western country.

Below historian Asvi Warman Adam explains what happened and the impact it had on Indonesia and global politics.

Who carried out the killings?

The army, with the help of civilian militias mostly from Islamic groups such as the Nahdlatul Ulama, or NU, carried out the murders of communists and their supporters.

The army trained the militias in Central and East Java with a directive to eradicate the PKI “down to its roots”. The militias interpreted this directive freely to encompass everything from arrest to murder.

Before the anti-communist crackdown, Muslim clerics and the PKI were already caught in conflict. The PKI and Indonesia Peasants Front (BTI) had been taking land from religious clerks and owners of Islamic boarding schools to be given to the state for land reform. Before October 1965, NU created a youth militia called Banser (an acronym for multi-purpose front).

Black campaigns that fuelled distrust between the two groups were also swirling around. A recent gathering of Syarikat, a youth NU organisation working on truth and reconciliation for 1965 crimes, revealed that people from NU received a list of their names to be killed by PKI and vice versa. Neither side had a clue about the creator and distributor of the hit lists. It is not hard, however, to suspect the culprit.

What triggered the downfall of the PKI?

In Pretext for Mass Murder, historian John Roosa has provided the most comprehensive analysis on the events of 1965.

In the years leading to October 1965, there were three significant powers in Indonesia: Sukarno, the army, and its rival the PKI. A charismatic independence leader, Sukarno held the powers in balance.

The PKI placed fourth out of 172 political parties in the country’s first national election in 1955. They were popular among farmers because of their programs on land reform.

Meanwhile, the army’s political power was also rising following their victory in crushing regional uprisings in 1958. In July 1959, Sukarno released a presidential decree to return to the 1945 Constitution, giving the military seats in the People’s Consultative Assembly.

By 1965, the balance between Sukarno, the army and the PKI became disturbed for three reasons. First, the army and PKI were concerned about Sukarno’s health after he suffered a mild stroke in August 1965.

Second, suspicions about army’s disloyalty grew after a letter allegedly written by British ambassador Andrew Gilchrist surfaced in May 1965. The letter raised the prospect of a joint military intervention in Indonesia with the US that would involve “our local army friends”. Third, there were rumours about a “Generals' Council”, a group of generals meeting in secret that were planning to stage a coup against Sukarno on October 5, 1965.

The PKI politburo, collaborating with officers from the presidential guard, decided to carry out a pre-emptive move by kidnapping members of the so-called “Generals' Council”. But the operation went horribly wrong. Instead of arresting the generals to be brought to Sukarno, they killed the generals and dumped the bodies in an unused well.

The operation – the “30th September Movement" – was easily crushed in a matter of hours by Suharto, the commander of the army’s strategic reserve, who proceeded to carry out a witch-hunt against communists and left-leaning groups.

Where was Sukarno?

Sukarno did not exactly know what happened on the night of the September 30. On his way to the presidential palace from the residence of one of his wives, Dewi Sukarno, he saw unknown troops. Presidential guards decided to bring the president to Halim airbase. According to standard operational procedure, in emergency situations the president should be safeguarded to either an airbase or seaport.

At Halim airbase, Brigadier General Soeparjo, an officer that was part of the 30th September Movement, told the president about the movement that aimed to save Sukarno from a military coup. Soeparjo also told him that some of the kidnapped generals were shot. Upon hearing the report, Sukarno ordered the movement to stop.

Sukarno was aware of the anti-communist killings and condemned them. Between October and December 1965, he called for the killings to end. However, the army by then controlled the media and his speeches were no longer published in newspapers. He was still allowed to give speeches from October 1965 to February 1967. He was banned from giving speeches from then on until his death in 1970.

What was international community’s role in the killings?

In 1965, Western countries saw communists as their enemy. They knew of the mass murders but considered them a necessary evil. The Soviet Union mildly condemned the killings. Japan knew but kept silent.

Declassified US files show that the US supported the anti-communist operations in Indonesia by providing funds and radio devices. The US also gave a list of names of PKI members to the army to be killed.

The UK and Australia were also complicit. Declassified files from the UK showed that UK and Australia carried out covert operations to spread false, “black propaganda” to encourage hostility against the PKI. The UK had an intelligence office in Singapore that they use to launch an anti-communism campaign.

How did the violence change Indonesia and the world?

The mass murder became a watershed moment for Indonesia. It transformed the country’s politics, economy and intellectual culture.

After the anti-communist massacre, Indonesia became very pro-Western. Previously it was an active player in the non-Aligned movement. Western and Japanese capital flowed into Indonesia, replacing economic co-operation with Eastern European countries.

Indonesia’s intellectual culture became uniform. During the era of Sukarno’s leadership there were many public debates between left- and right-wing intellectuals. In contrast, Suharto did not allow criticism and suppressed any dissent.

The destruction of communism in Indonesia benefited capitalist countries such as the United States and Japan. If the communists had come to power in Indonesia, the US forces in South Vietnam would have been surrounded by communist countries in Southeast Asia.

Prior to 1965, Japan, which occupied Indonesia in the second world war, had very little investment in Indonesia. But after the anti-communist massacre, it became the biggest foreign investor in Indonesia.

Will there be justice for the victims?

Indonesia’s National Human Rights Commission released a report in 2012 declaring the military responsible in gross human rights violation in 1965. There has yet to be a criminal inquiry.

However, there has been gradual progress in the political will of Indonesian leaders to resolving the 1965 tragedy.

In his election manifesto, Indonesian President Joko Widodo promised to solve past human rights abuses. He has incorporated this in his administration’s medium-term plan.

In his national address on August 2015, Widodo called for a national reconciliation. This is a step forward from his predecessor Susilo Bambang Yudhoyono. But how reconciliation will be carried out is yet to be seen.

This article was originally published on The Conversation.