America has gone through withdrawal phases before, usually after a great war: World War I, World War II, Korea and Vietnam. Some were longish, like the retreat between 1919 and the late 1930s. Some were brief, as after 1945, 1954 and 1975 (when the Vietnam War ended). In each case, war weariness translated into "Come home, America," as George McGovern famously proclaimed during the 1972 presidential campaign. In each case, the rebound eventually followed because the world wouldn't quite accommodate itself to America's reflexes. Fresh and old threats demanded American attention because others proved unable to fashion and secure a new balance of power.