History rarely announces the beginning of a new era; it reveals it afterward. Great conflicts rarely begin with a single event. They emerge gradually, through a series of crises that at first appear regional, disconnected and manageable. Nazi Germany and the Soviet Union had invaded and partitioned Poland, France had fallen, Britain was fighting for its survival, and Japan had been at war in China since 1937 when the Japanese attacked Pearl Harbor in December 1941. For Americans, the global war began at Pearl Harbor. For the world, it had begun years earlier. Could we be living through the early...