It was Henry Luce, the founder of Time, who in a signed editorial in his own magazine made popular the phrase “the American Century.” The century was then already more than two-fifths over. It was 1941, and the Japanese had not yet attacked Pearl Harbor. The argument rumbled on whether the United States should enter the war on the side of Britain against Japanese militarism and German and Italian fascism, as President Franklin Delano Roosevelt privately thought inevitable, or should remain neutral, as a majority of both Congress and public opinion still preferred.

Luce wrote of the American Century not out of triumphalist nationalism but as a prophet calling on his countrymen to take up a burden in the spirit of Christian sacrifice. America should save Britain, Luce said, but, more than that, “we must undertake now to be the Good Samaritan of the entire world.” He saw his country as destined to lift mankind “from the level of the beasts to what the Psalmist called a little lower than the angels.” The history of the rest of the American century can be seen as a commentary on the extent to which Luce's countrymen lived up to his vision, at home and abroad.