Robert Higgs writes, "Many people are misled by formalities. They assume, for example, that the United States went to war against Germany and Japan only after its declarations of war against these nations in December 1941. In truth, the United States had been at war for a long time before making these declarations. Its warmaking took a variety of forms. For example, the U.S. navy conducted "shoot [Germans] on sight" convoys, which might include British ships, in the North Atlantic along the greater part the shipping route from the United States to Great Britain, even though German U-boats had orders to refrain (and did refrain) from initiating attacks on American shipping. The United States and Great Britain entered into arrangements to pool intelligence, combine weapons development, test military equipment jointly, and undertake other forms of war-related cooperation. The U.S. military actively cooperated with the British military in combat operations against the Germans, for example, by alerting the British navy of aerial or marine sightings of German submarines, which the British then attacked. The U.S. government undertook in countless ways to provide military and other supplies and assistance to the British, the French, and the Soviets, who were fighting the Germans. The U.S. government provided military and other supplies and assistance, including warplanes and pilots, to the Chinese, who were at war with Japan. The U.S. military actively engaged in planning with the British, the British Commonwealth countries, and the Dutch East Indies for future combined combat operations against Japan. Most important, the U.S. government engaged in a series of increasingly stringent economic warfare measures that pushed the Japanese into a predicament that U.S. authorities well understood would probably provoke them to attack U.S. territories and forces in the Pacific region in a quest to secure essential raw materials that the Americans, British, and Dutch (government in exile) had embargoed."
Truncating the Antecedents by Robert Higgs