In the weeks before they surrendered control of Khartoum, the Rapid Support Forces sometimes took revenge on civilians. If their soldiers lost territory to the Sudanese Armed Forces during the day, the militia’s commanders would turn their artillery on residential neighborhoods at night. On several consecutive evenings in March, we heard these attacks from Omdurman, on the other side of the Nile from the Sudanese capital. From an apartment that would in better times have been home to a middle-class Sudanese family, we would hear one explosion. Then two more. Sometimes a response, shells or gunfire from the other side....