The Americans move their Pacific Fleet from California to Hawaii

In early 1940, Japan began to fortify the Marshall Islands which lie in the central Pacific between Hawaii and the Philippines. The threat to American communications between Hawaii and the Philippines caused President Franklin D. Roosevelt in June 1940 to order the United States Pacific Fleet to move its main Pacific base from California to Pearl Harbor in the Hawaiian Islands. The move was designed to demonstrate the naval power available to the United States in the Pacific region, and hopefully, to act as a deterrent to Japanese aggression against American, British and Dutch colonial possessions in East Asia. The move was not without significant risk, however, because it placed the American Pacific fleet within striking distance of Japan's powerful navy.


By signing the Tripartite Pact on 27 September 1940, Japan allied itself
with the European Axis Powers, Nazi Germany and fascist Italy.

In response to the menace of Hitler, the United States decides to rebuild its navy

With the fall of France to Adolf Hitler's Nazi armies in June 1940, President Roosevelt was finally able to persuade Congress to approve a massive expansion of the United States Navy by passing the Vinson-Walsh "Two Ocean Navy Act". This expansion program would enable the United States to retire many of its old warships and permit establishment of separate Pacific and Atlantic fleets.

President Roosevelt resolves to support Britain against Nazi Germany

In the week preceding the 1940 Presidential election, Franklin D. Roosevelt gave the American people a solemn promise that no American "boys" would be sent to fight in Europe. Less than two weeks after he won an unprecedented third term in office, President Roosevelt received a private briefing from the Chief of Naval Operations, Admiral Harold R. Stark, that shattered the foundation for his promise. Admiral Stark warned Roosevelt that failure by the United States to aid Britain against Germany would almost certainly lead to Britain's defeat and German domination of the whole of Europe, the Middle East and Africa. Stark argued that American aid to Britain should include actual participation in the war in Europe and North Africa by US armed forces. Stark also argued that top priority should be given to defeating Germany regardless of any threat that might arise from Japan.

Roosevelt realized that the scenario painted by Admiral Stark would result in the domination of Europe, Africa and Asia by the three Axis powers and leave the Americas isolated. The countries of Central and South America would be likely to choose neutrality, and so leave the United States and Canada alone to face any threat from the three Axis powers. The economic cost of this outcome to the United States would be ruinous. If Roosevelt needed any further incentive to assist Britain, it was provided in letters from the world famous physicist Albert Einstein who warned Roosevelt that Nazi Germany was working on the development of a weapon of enormous destructive power, namely, an atomic bomb!

Admiral Stark's advice that the defeat of Nazi Germany should be the top priority of the United States even in the event of war with Japan was accepted by President Roosevelt, and formally accepted as "Plan D". The plan acquired the designation "D" simply because it followed the numbering in Stark's formal memorandum to the President. The US Army Chief of Staff, General George C. Marshall, supported the "Germany first" plan and Roosevelt authorized talks between the American and British military chiefs of staff to implement Plan D. The "Germany first" strategy was not announced to the American public. The political risks would have been too great. Apart from attracting the fury of the powerful isolationist and peace lobbies, it would be an admission that America's army in the Philippines would be abandoned to its fate in the event of a Japanese attack.  

America becomes the arsenal of democracy

Before Pearl Harbor, President Roosevelt was restrained by Congress from any major effort to upgrade the fighting efficiency of America's defence forces. However, Roosevelt insisted that America had a moral obligation to assist Britain to survive the onslaught of Nazi Germany. Roosevelt declared that America would become the "arsenal of democracy". American-produced fighters and bombers were sold to Britain, and fifty World War I destroyers were lent to Britain under the President's "Lend Lease" plan. While this aid was being given, the isolationist and peace lobbies continued to insist that no American troops take part in the war in Europe.

Japan was aware that America had neglected its own defences

The American naval building program was viewed with deep suspicion by the Japanese who appreciated that the United States Navy would eventually replace theirs as the most powerful navy in the Pacific region. A powerful American fleet in the Pacific would jeopardise Japan's plans to seize American, British and Dutch colonial possessions in South-East Asia. Japan's military leaders decided that Japan must seize its target countries in South-East Asia before the United States could rebuild its navy.

Japan's greatest fighting admiral during World War II, Admiral Isoroku Yamamoto, had taken careful note of America's enormous industrial strength during two tours of duty in the United States. He had also noted that successive American governments had starved the defence forces of adequate funding. In planning his sneak attack on the United States Pacific Fleet at Pearl Harbor on 7 December 1941, Yamamoto was very conscious of the fact that America had neglected to maintain its fleet in top fighting condition. In a letter to a friend before he launched his attack on Pearl Harbor, Yamamoto wrote:

I shall run wild for the first six months or a year, but I have no confidence for the second and third years.

Yamamoto astutely realised that it would take the United States at least a year to gather its full military strength after two decades of neglect of its armed forces.* This realisation coloured his strategic planning, and influenced his two major preoccupations: the destruction of the US Pacific Fleet at Pearl Harbor and the placing of a Japanese steel noose around Hawaii so as to put 2,200 miles of unbroken ocean between America's likely naval strength in 1943 and Japan's eastern defensive perimeter anchored in Hawaii.

* In fact, it would take almost two years before this happened.

Japan declares a Greater East Asia Co-Prosperity Sphere

With war raging in Europe, and with Britain hard-pressed by Germany and Italy, the Japanese demanded in July 1940 that Britain halt the movement of war materials through Burma to the beleaguered Chinese Nationalist government which had retreated from the advancing Japanese troops to establish a wartime capital at Chungking in western China. The British government bowed to this Japanese demand. However, the Americans responded to the tightening of the Japanese noose around China by providing assistance to the Chinese Nationalist government and introducing restrictions on the sale of certain war-related raw materials to Japan, such as petroleum and scrap metal.

These economic sanctions only succeeded in hardening the attitudes of Japan's militarists, and increasing their hostility towards the United States, which they felt was meddling in Japan's natural sphere of interest in East Asia. The Japanese government responded publicly to the American economic sanctions by declaring its intention to expand the reach of its "New Order in East Asia" by establishing a Greater East Asia Co-Prosperity Sphere.

The New Order would now involve a Japanese-controlled political and economic grouping of countries for the purpose of supplying Japan with food and the raw materials needed by Japan's industries, particularly its war-related industries, and accepting Japanese exports in return. The countries listed by Japan for its New Order included the Philippines, Malaya (now Malaysia), Burma, Thailand, French Indo-China (now Vietnam), the Netherlands East Indies (now Indonesia), Australia and New Guinea. The Japanese made it quite clear that any country resisting inclusion in their Greater East Asia Co-prosperity Sphere would be treated as an enemy of Japan.

The announced Greater East Asia Co-prosperity Sphere did not disclose Japan's true intention which was to seize by military force America's Philippines, and resource-rich British and Dutch colonial possessions in South-East Asia.

As tensions increased between Japan and the United States, the Japanese began looking for allies who would support further military aggression by Japan in East Asia.

The Tripartite Pact 1940 - Japan allies itself with Nazi Germany and Fascist Italy

On 27 September 1940, Germany, Italy and Japan signed the Tripartite Pact. The agreement recognised Japan's self-assumed role in establishing a "New Order" in East Asia, and provided for mutual assistance should any one of the three powers be attacked by another country not already involved in the European conflict or the war in China. The Germans and Italians wanted the pact to convey a clear warning to the United States that it would face war with Japan if it entered the war in Europe on Britain's side. The Japanese did not tell their new allies that they were already preparing for war against the United States.

Japan signs a non-aggression pact with the Soviet Union

Being mindful of the need to protect Manchukuo from attack by the Soviet Union while Japan was attacking American, British and Dutch territory in South-East Asia, the Japanese Foreign Minister Matsuoka visited Moscow and signed an anti-aggression pact with the Soviet dictator Josef Stalin on 3 April 1941.

Prime Minister Konoye attempts to avoid war with the United States

The Japanese Prime Minister, Prince Fumimaro Konoye, still wanted to avoid war with the United States if it could be avoided. Konoye appointed Admiral Kichisaburo Nomura as ambassador to the United States in April 1941, and instructed him to attempt to reach an agreement with the Americans that would recognise Japan's predominance in East Asia.

Increasing Tensions between the United States and Japan during 1941

Tension between Japan and the United States increased dramatically when Japan seized French Indo-China (now Vietnam) in July 1941. Japanese troops poured into Indo-China, and the Japanese military began preparations to attack the Philippines and British and Dutch colonial possessions in South-East Asia. President Roosevelt responded to Japanese aggression in Indo-China by placing an embargo on the sale of American oil and petroleum 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 oil and rubber it needed to continue its undeclared war on China, and to pursue further military aggression in South-East Asia.

The Western economic embargoes 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 its puppet state Manchukuo, which had been the former Chinese territory of Manchuria. However, militarist hard-liners in Japan were not prepared to give ground on China or their proposed New Order in East Asia.

Japan's militarists prepare to seize American, British and Dutch territories

Once again, economic sanctions had failed. These measures only succeeded in hardening further the attitudes of Japan's militarists towards the United States. The hard-line militarists in Tokyo wanted war not a diplomatic settlement, and they replaced Prime Minister Konoye on 18 October 1941 with a hard-line militarist, General Hideki Tojo, who was eager for war with the United States.

On 5 November 1941, the Tojo government decided to attack the United States unless the Americans accepted all of Japan's demands by 25 November 1941. If the United States failed to meet that deadline, the Japanese intended to seize America's Philippines and resource-rich British and Dutch colonial possessions in South-East Asia. These countries would then be incorporated into the Japanese empire. All of these countries except the Philippines were either rich in raw materials, especially oil and rubber, needed by Japan's aggressive war machine or in food needed by Japan's fast-growing population.

The Philippines was a target for Japanese aggression simply because it belonged to the United States at this time and because it was strategically located between Japan and the countries of South-East Asia which Japan intended to seize.

Japan plans a surprise attack on the United States Pacific Fleet at Pearl Harbor

The United States Pacific Fleet based at Hawaii posed the only significant threat to JapanŐs aggressive territorial ambitions. To eliminate this risk, the Japanese government decided to launch a surprise air attack on the United States Pacific Fleet at its Pearl Harbor base on Sunday morning, 7 December 1941. The attack on Pearl Harbor would be timed to coincide with Japan's attacks on the Philippines and British Malaya.