...Having broken the Japanese diplomatic code, the Americans knew, among many other things, what Foreign Minister Teijiro Toyoda had communicated to Ambassador Kichisaburo Nomura on July 31: “Commercial and economic relations between Japan and third countries, led by England and the United States, are gradually becoming so horribly strained that we cannot endure it much longer. Consequently, our Empire, to save its very life, must take measures to secure the raw materials of the South Seas.”
Because American cryptographers had also broken the Japanese naval code, the leaders in Washington knew as well that Japan’s “measures” would include an attack on Pearl Harbor. Yet they withheld this critical information from the commanders in Hawaii, who might have headed off the attack or prepared themselves to defend against it. That Roosevelt and his chieftains did not ring the tocsin makes perfect sense: after all, the impending attack constituted precisely what they had been seeking for a long time. As Stimson confided to his diary after a meeting of the war cabinet on November 25, “The question was how we should maneuver them [the Japanese] into firing the first shot without allowing too much danger to ourselves.” After the attack, Stimson confessed that “my first feeling was of relief ... that a crisis had come in a way which would unite all our people.