There are some foreign-policy questions that require all the wisdom America's leaders can summon—and some good luck as well. Responding to China's emergence as a military and economic power, for instance, may prove as difficult for the international system as coming to terms with Germany's rise was in the last century, with the consequences for getting it wrong even more severe.
But until the last few years, no sensible American would have considered the Balkans such a question, or indeed a major issue at all for the United States. The complexity of the ethnic configurations, the depth of their historic enmities—these were at least generally known to most American students of diplomacy and were captured in various aphorisms and historical vignettes: "Not worth the bones of a single healthy Pomeranian grenadier" (attributed to Otto von Bismarck); "An area which produces more history than it can consume locally" (attributed to Winston Churchill). Or my favorite, from Churchill's Balkan envoy Fitzroy Maclean's account of a 1944 conversation with the prime minister, when the two discussed the implications of the communist leanings of the Yugoslav partisans then receiving Allied aid.
"Do you intend," [Churchill] asked, "to make Yugoslavia your home after the war?"
"No sir," I replied.
"Neither do I," he...