The Khmer Rouge killed nearly two million Cambodians from 1975 to 1979, spreading like a virus from the jungles until they controlled the entire country, only to systematically dismantle and destroy it in the name of a Communist agrarian ideal.

The Khmer Rouge took root in Cambodia’s northeastern jungles as early as the 1960s, a guerrilla group driven by communist ideals that nipped the periphery of government-controlled areas. The flash point came when Cambodia’s leader, Prince Norodom Sihanouk, was deposed in a military coup in 1970 and leaned on the Khmer Rouge for support.

When the Khmer Rouge succeeded in capturing the Cambodian capital of Phnom Penh in 1975, they evacuated the entire population of the city — more than 2.5 million people — to camps in the countryside. Similar evacuations took place every time the Khmer Rouge took over a new city.

Simultaneously, the Khmer Rouge were planning the steps necessary for a radical shift to an agrarian society. During the Khmer Rouge’s nascent days, the movement’s leader, Pol Pot, had grown to admire the way the tribes on the outskirts of Cambodia’s jungles lived, free of Buddhism, money or education, and now he wanted to foist the same philosophy on the entire nation.

Pol Pot envisioned a Cambodia absent of any social institutions like banks or religions or any modern technology. He sought to triple agricultural production in a year, absent the manpower or means necessary.

It’s impossible to tally the total number dead with any precision, but it is generally assumed that the Khmer Rouge killed between one million and two million people during their reign. Thousands more died of malnutrition or disease, and the upper classes of Cambodian society were all but wiped out. The killing continued unabated until Vietnamese troops, tired of border skirmishes with the Khmer Rouge, invaded in 1979 and sent the Khmer Rouge back to the jungles.