Would America turn inwards again, as it had after the First World War? That was the great question of the immediate post-War years, at least for Europeans, and it was underlined by some of President Truman's early actions. The question was to be answered clearly in the negative. Within five years the United States had taken on the leadership of an alliance that included most of Western Europe, and was soon to be extended in effect to the Western Pacific. This came about largely because the Soviet Union insisted on having complete control of Eastern Europe, while the United States insisted that governments must be freely elected. Differences over Germany and Eastern Europe quickly broke up the wartime coalition and started the Cold War. But Asia played a part in the process too. The victory of the Chinese Communists over the Nationalists, coinciding as it did with Soviet acquisition of atomic weapons, turned growing concern about Communism in America into widespread fear, verging at times on hysteria. The charge that the Democrats had ‘lost’ China made it necessary for Truman to defend South Korea when it was attacked by the Communist North, and bring Asia to the centre of the Cold War.

The defeat of Germany and Japan left America by far the most powerful country in the world. The war effort had mobilised resources that had not been fully used during the 1930s, and had increased production by 50 per cent. The American share of total world production had risen from the quarter to a third. This feat had been achieved while five million men were under arms, a large proportion of them deployed overseas. Britain had played a critical part in the early stages of the war, but it was largely American armies that had completed the defeat of Germany, just as it was the American navy and air force that completed the defeat of Japan. With the cooperation of Britain and other allies, the United States had made two atomic bombs, which it used to obviate an invasion of Japan.