"IN JANUARY 2012 A HUNDRED RAIDERS ON HORSEBACK CHARGED OUT OF CHAD INTO CAMEROON’S BOUBA NDJIDAH NATIONAL PARK, SLAUGHTERING HUNDREDS OF ELEPHANTS—entire families—in one of the worst concentrated killings since a global ivory trade ban was adopted in 1989. Carrying AK-47s and rocket-propelled grenades, they dispatched the elephants with a military precision reminiscent of a 2006 butchering outside Chad’s Zakouma National Park. And then some stopped to pray to Allah. Seen from the ground, each of the bloated elephant carcasses is a monument to human greed. Elephant poaching levels are currently at their worst in a decade, and seizures of...