This book’s title is drawn from a comment that a close ally of Sudanese President Omar al-Bashir made after South Sudan gained its independence from Sudan in 2011, as he bid good riddance to a region that had been like a “poisonous thorn” in Khartoum’s heart. But Copnall shows that the cultural, political, and economic links between the countries remain dense and complicated and argues that the two sides need to forge a productive relationship if either is to thrive. His own analysis suggests that is unlikely: the divides are deep, and the leaders in both countries are corrupt and repressive. Shortly after they parted ways, the two countries fought bitterly over territory as both governments clamped down on domestic dissent. Copnall’s many interviews with officials and ordinary people on both sides lend the book real authority and a sense of genuine empathy for the people of the two Sudans.