The war in Vietnam, spanning more than twenty years, was one of the most divisive conflicts ever to envelop the United States, and its complexity and consequences did not end with the fall of Saigon in 1975. As Peter Sills demonstrates in Toxic War, veterans faced a new enemy beyond post-traumatic stress disorder or debilitating battle injuries. Many of them faced a new, more pernicious, slow-killing enemy: the cancerous effects of Agent Orange.

Originally introduced by Dow and other chemical companies as a herbicide in the United States and adopted by the military as a method...