That’s not the only, or even the worst, legacy of the war that Vietnamese families still face. Seeking to defoliate entire forests to expose enemy forces to spotter planes, the Americans dropped 18 million gallons of chemical herbicide over South Vietnam from 1962 to 1972. There were several defoliants used, but the best known was Agent Orange. In 20,000 spraying missions, planes drenched the countryside and an estimated 3,181 villages.

While entire forests dried up and died typically within weeks of spraying, it would be years before scientists established that one of the active ingredients in the defoliants, a group of compounds called dioxin, is one of the deadliest substances known to humankind. Just 85 grams of dioxin, if evenly distributed, could wipe out a city of eight million people. But illnesses and deaths from Agent Orange exposure were only the initial outcomes. Dioxin affects not only people exposed to it, but also their children, altering DNA. Large numbers of Vietnamese babies continue to be born with grotesque deformities: misshapen heads, bulging tumors, underdeveloped brains and nonfunctioning limbs.

The deadly defoliants also rained down on American troops. Researchers led by Jeanne Stellman of Columbia examined military records of the flight paths of Agent Orange spraying missions. Comparing those flight paths to the position of nearby villages and American ground troops revealed a direct association between exposure and later health problems.