Increasing tensions between the United States and Japan during 1941

Tensions between Japan and the United States increased dramatically when Japan seized French Indochina (now Vietnam) in July 1941. President Roosevelt responded to that aggression by imposing an embargo on the sale of American oil to Japan, and freezing Japan's assets in the United States. The British government and the Dutch government-in-exile followed the lead of the United States in imposing economic sanctions on Japan. By August 1941, Japan faced an almost total embargo on the military-related imports it needed to continue its brutal and undeclared war on China, including oil and rubber.

The Western economic embargoes had placed Japan in a very difficult position. While a large strategic reserve of oil had been accumulated in Japan, this would only last two years without replenishment from outside sources. The Americans were only insisting that Japan withdraw its invading troops from China and abandon its plan for forced incorporation of countries in its Greater East Asia Co-Prosperity Sphere. The Americans were not insisting that Japan withdraw from the vast former Chinese territory of Manchukuo. However, militarist hardliners in Japan were not prepared to give ground on China or their proposed New Order in East Asia.

Japan's militarists decide to launch a surprise attack on the United States

Once again, economic sanctions had failed. These measures only succeeded in hardening the attitudes of Japan's militarists, and increasing their determination to attack the United States. The Japanese Prime Minister, Prince Fumimaro Konoye, hoped to avoid war and reach an agreement with the United States that would acknowledge Japan's predominance in East Asia. However, the militarists wanted war not a diplomatic settlement, and on 17 October 1941, they forced the replacement of Prince Konoye with a hard-line militarist, General Hideki Tojo.

Japan's militarist Prime Minister, General Hideki Tojo, wanted war with Great Britain and the United States. He was executed as a war criminal after Japan's defeat.

Japan then sent a special envoy, Saburo Kurusu, to the United States to assist Japan's Ambassador, Admiral Kichisaburo Nomura, in engaging the attention of the Americans in diplomatic manoeuvring while the Japanese completed their preparations for attacking the United States Pacific Fleet at its Pearl Harbor base. On 3 November 1941, Admiral Nagano, Chief of the Japanese Naval General Staff gave his approval to Admiral Yamamoto's plan for the attack on Pearl Harbor.

The Japanese carrier strike force departs for Hawaii

A strike force comprising six of Japan's largest fleet aircraft carriers and supporting warships left Japan on 26 November 1941. Preserving strict radio silence, the strike force headed for a stand-by point located about 1,000 miles (1.600 km) north of Hawaii. At the stand-by point, the strike force would either receive confirmation to attack the United States Pacific Fleet at Pearl Harbor or be instructed to return to Japan.

Japan's Prime Minister Hideki Tojo threatens Britain and the United States with war

In the last week of November 1941, the American Secretary of State, Mr Cordell Hull handed Japan's special envoy, Mr Saburo Kurusu, a document outlining American proposals for resolving the serious differences that had arisen between the United States and Japan in East Asia. The American document called on Japan to withdraw its troops from China and abandon its plan for forced incorporation of countries into its proposed Greater East Asia Co-Prosperity Sphere. Three days later, at a time when Japanese aircraft carriers were already sailing towards Pearl Harbor with hostile intent, Japan's Prime Minister and Minister for War, General Hideki Tojo, rejected the American proposals and issued a sharp warning to Britain and the United States that Japan would "purge East Asia of US -British power with a vengeance".

General Tojo's threat appeared on the front page of the New York Herald Tribune on Sunday, 30 November 1941, exactly seven days before the Japanese attack on the United States Pacific Fleet at Pearl Harbor.

Despite the threat of war contained in Tojo's warning, and despite having no firm knowledge of the whereabouts of Japan's six largest fleet aircraft carriers, no significant steps were taken at Hawaii to place the United States Pacific Fleet and the Army/Air Force on full war alert. The Americans had broken the Japanese diplomatic code in September 1941, and knew that Tokyo had warned its envoys in Washington that certain unspecified events would occur after 29 November 1941. However, the Americans believed that the warning foreshadowed a move by the Japanese against British or Dutch possessions in South-East Asia, or possibly, the Philippines. Despite the clear danger to the Philippines, the American army commander in the Philippines, General Douglas MacArthur, took no effective steps to bring his air force and armies to a state of war readiness.