It’s certainly not for lack of power. From 1846 to 1945, the United States had a minuscule peacetime army, but won almost every major campaign. After World War II, Washington constructed the most expensive military machine that ever existed and endured seven decades of martial frustration. Indeed, power is part of the reason the United States loses. After 1945, America’s newfound strength created a constant temptation to use force, and projected U.S. forces into distant conflicts. But Washington chose an unfortunate moment to discover its inner interventionist. The nature of global warfare changed in ways that made military campaigns ugly at best and unwinnable at worst.