In 1994 Rwanda was scarred by an organized campaign of mass carnage perpetrated by the Hutu majority against the Tutsi minority and moderate Hutus. It was the final genocide of the twentieth century, with the killers murdering about one million people in about 100 days. The United Nations and U.S. looked on but failed to act, a tragic misstep that has influenced decision-makers since to look differently at the task of intervening in foreign conflicts to protect the innocent. In this episode, Omar McDoom of the London School of Economics and Political Science, a scholar of genocide and expert on central Africa, reflects on the enduring lessons of Rwanda's darkest hour.