In 1965, Indonesia was the setting of one of the largest massacres of the twentieth century. The army halted the rapid rise of the Communist Party at the cost of around 500,000 lives. Little studied before the fall of the dictator Suharto (1998), we gradually unravel the complexity of the event: a node in the Cold War in the Far East, a battle for power between the two most well-organized groups in the country, it was also an act of social vengeance, and particularly the means for channeling a twentieth century religious war that pitted believers against "atheists." Both supervised and spontaneous, not very evenly distributed spatially, and hallmarked by acts of brutality, it was more of a pogrom on a terrifying scale than an extermination campaign.