This article appears in print in the September 2018 issue. Click here to subscribe.

It’s been called “The Great War,” as if there’d never be a bigger one.

Although its origin was almost comically trivial—because of tangled alliances, the assassination of one archduke pulled an entire continent and beyond into conflict—the casualties were unprecedentedly hideous, due to chemical weapons; related epidemics, revolutions and genocides killed millions more.