In December 2023, when South Africa accused Israel of genocide before the International Court of Justice, I thought it was wrong to do so. Israel had been attacked. Its defense was legitimate. The blood was on Hamas’s hands. But over the last year, I have watched a slew of organizations and scholars arrive at the view that whatever Israel’s war on Gaza began as, its mass assault on Palestinian civilians fits the definition of genocidal violence. This is a view now held by Amnesty International, B’Tselem, Human Rights Watch, and the president of the International Association of Genocide Scholars, among many others One reason I have stayed away from the word genocide is that there is an imprecision at its heart. When people use the word genocide, I think they imagine something like the Holocaust: the attempted extermination of an entire people. But the legal definition of genocide encompasses much more than that. So what is a genocide? And is this one? Philippe Sands is a lawyer who’s worked on a number of genocide cases. He is the author of, among other books, “East West Street,” about how the idea of genocide was developed and written into international law. He is the best possible guide to the hardest possible topic.