There is no one date that can be said to mark the beginning of the greatest of global conflicts. In 1931, the Japanese army invaded Manchuria, a northern province of China. In July 1937, the Japanese moved again, this time directly against the Nationalist regime of Chiang Kai-shek. The atrocities that followed shocked the world. Meanwhile, in 1936, German Chancellor Adolf Hitler moved aggressively into the Rhineland, previously a demilitarized zone, and in 1938, he incorporated Czechoslovakia and Austria into the Third Reich. By this time, the Western world was fully alert to the menace of the fanatically ambitious and confident Fuhrer. Then, in the early morning hours of September 1, 1939, Hitler sent his armies into Poland. Two days later, France and Great Britain declared war on Germany. Within a matter of weeks the Soviet Union, which had recently signed a non-aggression treaty with Hitler, attacked Poland from the east. Within a month, Polish resistance collapsed, and Warsaw fell. World War II had begun.
In general, the American people did not want to have any part in a European war. They felt protected by great oceans on both sides of the North American continent. And they felt that, in World War I, American boys had fought and bled in France mostly to make fortunes for munitions makers and arms merchants. Moreover, the United States had allowed its armed forces to wither in the 1920s and 1930, so that when World War II broke out in Europe, its army of 190,000 men ranked about eighteenth in the global rankings, about on a par with Rumania and Bulgaria.
World War II was the central event of the twentieth century. It involved all six major continents, all three of the great oceans on the planet, scores of countries, and billions of people. It caused 57 million deaths and unimaginable human suffering. It brought about the redrawing of national boundaries in Europe and Asia, forced the relocation of many ethnic groups, made millions of families homeless,...