It's easy to mock The Golden Arches Theory—the idea that if two countries have McDonalds, they won't go to war—but let's do it anyway. The idea was first proposed back in 1996 by Thomas L. Friedman, The New York Times columnist, and he was hardly the only person who bought it. The capitalism=democracy thinking that underpinned the theory had been in vogue since the Cold War, and its proponents were ascendent in the 1990s following the collapse of the Soviet Union. Once someone got a taste of American business, then they'd have to support American democracy, the thinking went. Free...