“My last film was on the US and the Holocaust,” documentarian Ken Burns told an audience in Washington recently. “I didn’t think the next film would be about eugenics too.” That next film is The American Buffalo, a two-part, four-hour series exploring how the national mammal helped sustain Native Americans on the Great Plains for millennia – only to be nearly wiped out by white settlers in little more than a decade. The documentary quotes historian Dan Flores as saying: “There is no story anywhere in world history that involves as large a destruction of wild animals as happened in...