A decade ago, when David Armitage began working on his new book, Civil Wars: A History in Ideas, published this week by Knopf, he had no idea how relevant the subject would become. These days, it’s hard to avoid concluding that American society is tearing itself apart. Several observations and arguments in the book can be harrowing to read—that the nations mostly likely to devolve into civil wars are those that have suffered such conflicts before; that civil wars are most likely when the government is divided against itself; that politics is civil war by other means. Civil Wars ranges over more than two millennia of history, law, and philosophy, but it feels as urgent as the latest shock, as fresh as tomorrow’s news. 

I recently spoke with Armitage about his book. The conversation has been lightly edited.

This book is a story of paradox, from the first page to the last. Can you explain why the very idea of “civil war,” beginning with the Romans, is a bundle of contradiction?

The Romans were the first to call this kind of conflict “civil wars.” The literal term “civil” comes from the Latin word cives, which means citizens. Romans named wars after the enemy they were fighting, so in this particular case, to call a war “civil” recognized that it was fought against a particularly familiar, even familial, enemy within Rome itself. Why was this paradoxical? Because the Roman definition of war hinged on it being fought for a just cause against an external enemy. To have a war against fellow citizens was to have a war that was not any kind of recognizable form of warfare at all. This was paradoxical, perhaps even oxymoronic, and it accounts for the fact that for several decades after the term was first recorded it was used very sparingly. “Civil war” is almost like the war that cannot speak its name. Romans didn’t want to recognize that they had descended to this destructive form of enmity against their own citizens. Even Julius Caesar, Rome’s most famous civil warrior, doesn’t use the term civil war in the context of his own history, an indication of his reluctance to deploy this deeply unsettling description of contention among the Romans who themselves invented it.

Romans didn’t want to recognize that they had descended to a destructive form of enmity against their own citizens. ...