The Secretary of Defense Can’t Go AWOL. Neither Can America.

A decade ago, I wrote a book with the subtitle “The New Isolationism and the Coming Global Disorder.” I’ve been wrong about a thing or two (or three) over the years. I wish I had been wrong about this.

Disorder comes in two varieties: disorder within a system (like a coup or revolution inside a sovereign state) or of the system itself (like the de facto collapse of the state system throughout parts of Africa and the Middle East). The former may be devastating, but it is usually containable. The...