<P> At least as early as October 8, 1940,...affairs had reached such a state that the United States would become involved in a war with Japan ...' that if the Japanese attacked Thailand, or the Kra Peninsula, or the Dutch East Indies we would not enter the war, that if they even attacked the Philippines he doubted whether we would enter the war, but that they (the Japanese) could not always avoid making mistakes and that as the war continued and that area of operations expanded sooner or later they would make a mistake and we would enter the war .'...</P> <P> Japan's 1940 move into Vichy - controlled Indochina further raised tensions . When combined with its war with China, withdrawal from the League of Nations, alliance with Germany and Italy and increasing militarization, the move provoked an attempt to restrain Japan economically . The United States embargoed scrap metal shipments to Japan and closed the Panama Canal to Japanese shipping . This hit Japan's economy particularly hard because 74.1% of Japan's scrap iron came from the United States in 1938 . Also, 93% of Japan's copper in 1939 came from the United States . In early 1941, Japan moved into southern Indochina, thereby threatening British Malaya, North Borneo and Brunei . </P> <P> Japan and the U.S. engaged in negotiations during the course of 1941 in an effort to improve relations . During these negotiations, Japan considered withdrawal from most of China and Indochina after drawing up peace terms with the Chinese . Japan would also adopt an independent interpretation of the Tripartite Pact, and would not discriminate in trade, provided all other countries reciprocated . However, these compromises in China were rejected by General Tojo, then War Minister . Responding to Japanese occupation of key airfields in Indochina (July 24) following an agreement between Japan and Vichy France, the U.S. froze Japanese assets on July 26, 1941, and on August 1 established an embargo on oil and gasoline exports to Japan . The oil embargo was an especially strong response because oil was Japan's most crucial import, and more than 80% of Japan's oil at the time came from the United States . </P> <P> Japanese war planners had long looked south, especially to Brunei for oil and Malaya for rubber and tin . In the autumn of 1940, Japan requested 3.15 million barrels of oil from the Dutch East Indies, but received a counteroffer of only 1.35 million . The Navy was (mistakenly) certain any attempt to seize this region would bring the U.S. into the war, but the complete U.S. oil embargo reduced Japanese options to the seizure of southeast Asia before its existing stocks of strategic materials were depleted, or submission to American demands . Moreover, any southern operation would be vulnerable to attack from the Philippines, then a U.S. commonwealth, so war with the U.S. seemed necessary in any case . </P>

Why did the us imposed an oil embargo on japan