When the first survivors’ accounts came out of Israel’s kibbutzim, I had the terrible sense that I had heard them before. And I had, in South Sudan. More than two decades earlier, I traveled to Sudan to witness Christian Solidarity International freed 2,952 black Africans from slavery. My American Anti-Slavery Group had helped raise funds to buy back their freedom. The freed slaves told us that the raiders came at dawn, screaming “Allahu akbar!” and murdered at will. They gang-raped the women and girls, then dragged them off as captives to use as concubines, domestics, or to sell. On October...