<P> The Philippines, at that time an American territory, were also a Japanese target . The Japanese military concluded an invasion of the Philippines would provoke an American military response . Rather than seize and fortify the islands, and wait for the inevitable U.S. counterattack, Japan's military leaders instead decided on the preventive Pearl Harbor attack, which they assumed would negate the American forces needed for the liberation and reconquest of the islands . </P> <P> Planning for the attack on Pearl Harbor had begun in very early 1941, by Admiral Isoroku Yamamoto . He finally won assent from the Naval High Command by, among other things, threatening to resign . The attack was approved in the summer at an Imperial Conference and again at a second Conference in the fall . Simultaneously over the year, pilots were trained, and ships prepared for its execution . Authority for the attack was granted at the second Imperial Conference if a diplomatic result satisfactory to Japan was not reached . After final approval by Emperor Hirohito the order to attack was issued at the beginning of December . </P> <P> Tensions between Japan and the prominent Western countries (the United States, France, Britain and the Netherlands) increased significantly during the increasingly militaristic early rule of Emperor Hirohito . Japanese nationalists and military leaders increasingly influenced government policy, promoting a Greater East Asia Co-Prosperity Sphere as part of Japan's alleged "divine right" to unify Asia under Hirohito's rule . </P> <P> During the 1930s, Japan's increasingly expansionist policies brought it into renewed conflict with its neighbors, Russia and China (Japan had fought the First Sino - Japanese War with China in 1894--95 and the Russo - Japanese War with Russia in 1904--05; Japan's imperialist ambitions had a hand in precipitating both conflicts). In March 1933, Japan withdrew from the League of Nations in response to international condemnation of its conquest of Manchuria and subsequent establishment of the Manchukuo puppet government . On January 15, 1936, Japan withdrew from the Second London Naval Disarmament Conference because the United States and Great Britain refused to grant the Japanese Navy parity with theirs . A second war between Japan and China began with the Marco Polo Bridge Incident in July 1937 . </P>

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