This volume of The Cambridge History of America and the World opens as World War II ends and the United States stands at the pinnacle of its power relative to the rest of the world. Indexes of that power abound: In 1950, for instance, the United States accounted for only 6.0 percent of the world population – but 27.3 percent of all economic activity (and a far larger share of industrial production), along with 66.3 percent of world military expenditure. Other forms of American global power were just as significant but harder to measure: the United States had taken the lead diplomatically, treating wartime allies like England and France as junior partners; it took a harsher attitude toward its other major wartime ally, the USSR. Economic and military strength, along with the ability to shape world politics – these very real and concrete forms of global power – were hardly the only dimensions of American power in the decades since World War II.