What all these collapsed powers have in common is that the complex social systems that underpinned them suddenly ceased to function. One minute rulers had legitimacy in the eyes of their people; the next they didn’t.

This process is a familiar one to students of financial markets. Even as I write, it is far from clear that the European Monetary Union can be salvaged from the dramatic collapse of confidence in the fiscal policies of its peripheral member states. In the realm of power, as in the domain of the bond vigilantes, you’re fine until you’re not fine—and when you’re not fine, you’re suddenly in a terrifying death spiral.

I find Ferguson’s “killer app” concept to be gratingly cute, but I see the point he’s making: we in the West have allowed the things that made us great to decay, relative to much of the rest of the world. He wonders what our “oh s**t” moment is going to be, when we wake up and realize what’s at stake. I would guess an economic catastrophe that causes a system collapse — for example, cascading European sovereign defaults that cause major European banks to go down, triggering credit-default swaps that bring down two or more major US banks. All this could happen in a month or two. It might not, but it could.