Al-Qaida is a terrorist threat, but it never had any hope of defeating us -- only of terrorizing us. And it hasn't been able to carry out an attack on U.S. soil since 9/11.
Our enviable strategic position gives us plenty of room to reduce defense outlays without compromising our safety or inviting attacks on our allies. It's hard to see any remaining military threat to Germany or the other countries of Western Europe that our forces ostensibly protect. Nor do we need troops there for one of NATO's original purposes: to keep the Germans under firm control.
Japan and South Korea may face genuine threats (China and North Korea), but they have ample resources to manage them. Japan has the world's third-biggest economy. South Korea's economy, which ranks 15th, is 80 times bigger than North Korea's.
But our allies punch below their weight. The U.S. spends 4.7 percent of its gross domestic product on defense. Japan spends just 1 percent, and South Korea 2.8 percent. In Germany, the figure is 1.3 percent. They have no reason to spend more as long as they can free-ride.
Would our permanent pullback from Europe and Asia change the strategic environment? Certainly. But after decades of American protection, our friends can form their own alliances to confront any adversary, present or future.
Worries about China and uncertainty about U.S. intentions have already moved Japan in that direction. "We want to build our own coalition of the willing in Asia to prevent China from just running over us," Yoshihide Soeya, director of the Institute of East Asian Studies at Keio University, told The New York Times.
We could foster more such efforts by our allies to work together to defend themselves. Or we could go broke doing it for them.