How genocide is defined—and why it’s so difficult to prove

The gravest of international crimes was outlawed in the 1940s after the atrocities of the Holocaust. But it took decades to convict anyone of genocide—and the term has since become a political weapon.

Genocide arose as a legal concept in the 1940s, coined by a jurist who believed the existing laws of war were inadequate. It has since been used to describe atrocities like the Khmer Rouge's killing of about 1.7 million people—including those pictured here—in late 1970s Cambodia.
Photograph by Manuel Cenata, Getty Images

United Nations chief Ban Ki-moon regularly spoke to international leaders and powerful diplomats. But in 2014, he faced a very different audience: a stadium filled with 30,000 anguished Rwandans who, two decades earlier, had seen more than 800,000 of their fellow citizens massacred in a hundred days of terror that have since been recognized as a genocide.

“We must not be left to utter the words ‘never again,’ again and again,” said Ban, as survivors screamed and sobbed.

The Rwandan massacre was the first time in history that an international tribunal had convicted anyone of genocide—a crime whose definition was only formalized in the wake of the Holocaust. Russia’s 2022 invasion of Ukraine has rekindled modern debates about the definition

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