I am a historian, and that usually means I’m a killjoy. When people say we’re at a unique moment in history, the historian’s job is to put things in perspective by pointing out that there is more continuity than discontinuity, that we are not special, that we think our moment is unique because we are narcissists and we’re at this moment. But what we are going through now—the past 20 or 30 years, and the next 20 or 30 years—really is historically unique. It is arguably the largest economic disruption in recorded human history. And our politics are not yet up to the challenge.

There...