In 2013, the largest Ebola outbreak in history swept across West Africa, claiming thousands of lives in Liberia, Sierra Leone, and Guinea and sending the international community into panic. By 2014, experts were grimly predicting that millions would be infected within months, and a huge international control effort was mounted to contain the virus. Yet paradoxically, at this point the disease was already going into decline in Africa itself. Why did outside observers get it so wrong?

Paul Richards draws on his extensive firsthand experience in Sierra Leone to argue that the international...