By the summer of 1941, as the United States was beginning to strengthen the Philippines, Japan had reached "the crossroads of her fate." The economic sanctions imposed by America, Great Britain, and the Netherlands had cut her off from the strategic materials necessary to support the war in China and threatened eventually to so weaken the Japanese economy as to leave Japan defenseless in a struggle with a major power. The leaders of Japan were faced with a difficult choice. They could either reach agreement with the United States by surrendering their ambitions in China and southeast Asia, or they could seize Dutch and British possessions by force.

The second course, while it would give Japan the natural resources so sorely needed, almost certainly meant war with Great Britain and the Netherlands. In the view of the Japanese planners, the United States would also oppose such a course by war, even if American territory was not immediately attacked. Such a war seemed less dangerous to Japan in the fall of 1941 than ever before and, if their calculations proved correct, the Japanese had an excellent chance of success. The British Empire was apparently doomed and the menace of Russian action had been diminished by the German invasion of that country and by the Japanese-Soviet neutrality pact.

The area marked for conquest formed a vast triangle, whose east arm stretched from the Kuril Islands on the north, through Wake, to the Marshall Islands. The base of the triangle was formed by a line connecting the Marshall Islands, the Bismarck Archipelago, Java, and Sumatra. The western arm extended from Malaya and southern Burma through Indochina, and thence along the China coast. The acquisition of this island-studded area would give to Japan control of the resources of southeast Asia and satisfy the national objectives in going to war. Perhaps later, if all went well, the area of conquest could be extended. But there is no evidence that it was the intention of the Japanese Government or of the Army and Navy to defeat the United States, and so far as is known no plan was ever drawn up for that purpose. Japan apparently planned to fight a war of limited objectives and, having gained what it wanted, expected to negotiate for a favorable peace.