Why did Japan attack Pearl Harbor? The reasons for the Japanese attack on Pearl Harbor had been building for some time motivated by the belief that Japan was destined to dominate Eastern Asia and the Pacific. The Japanese military had taken control of the civilian government and the militarists had adopted an aggressive policy of expansion seizing Manchuria in northern China in 1931.

FDR adopted economic policies to prevent further Japanese aggression in Southeast Asia introducing embargoes of steel, iron and oil against Japan and restricting the sale of war materials. In 1940 the US froze all Japanese assets and bank accounts in the US and Congress passed the Naval Expansion Act to triple the size of the US naval fleet by 1944. The US Pacific fleet was then moved in 1940 from California to Pearl Harbor as a further deterrent to Japanese aggression in the western Pacific. In August 1941 the US imposed an embargo on oil shipments to Japan. The Japanese responded by attacking the US naval fleet at Pearl Harbor.

Why did Japan attack Pearl Harbor?
Franklin Roosevelt was the 32nd American President who served in office from March 4, 1933 to April 12, 1945. One of the important events during his presidency was the Japanese attack on Pearl Harbor, Hawaii. Discover the history between Japan and the United States and why the Japanese, with a smaller land area than California and half the population of the US, attack the United States at Pearl Harbor.

Events Leading to the Japanese Attack of Pearl Harbor in Hawaii
This article provides comprehensive details of events leading to the Japanese Attack of Pearl Harbor in Hawaii including the background history of the relationship between Japan and America with important dates and events that led to the surprise bombing of the US Pacific Fleet at Pearl Harbor in Hawaii on Sunday, December 7, 1941. Refer to the Pearl Harbor Timeline and Pearl Harbor Facts.

Facts about Why did Japan attack Pearl Harbor
The following fact sheet contains interesting facts and information on Why did Japan attack Pearl Harbor.

History: Before the 1850s Japan had historically operated under a policy of isolationism which prohibited contact with most outside countries. The military force of America and their "Gunboat Diplomacy" put pressure on Japan to open itself to foreign trade. Refer to the Kanagawa Treaty

Following WW1 the relationship between the United States and Japan was marked by increasing tension due to territorial claims in the Pacific and U.S. treatment of Japanese immigrants.

The 1924 Immigration Act prohibited Japanese immigration into the US. Many Japanese were deeply offended by the new law and saw these actions as highly provocative

The history of tensions between Japan and the west continued. Japan believed that Western culture, European and American, was harmful to the culture, traditions and values of the Japanese people.

Japan adopted an Asia-centric position emphasizing Asian culture and traditions and rejecting western influence. The ‘ABCD Powers’ (America-British-Chinese-Dutch) were portrayed as a threat to the Japanese Empire.

The government system of Totalitarianism was introduced that asserted absolute and total control over the public and private lives of its citizens.

Due to the lack of natural resources in Japan, raw materials such as iron, oil, and coal largely had to be imported. Japan's economy was largely reliant on silk exports.

The Japanese did not want to rely on foreign imports. They wanted to create a colonial empire by conquering countries rich in natural resources

The Great Depression of the 1930s, worsened Japan's already poor economic state as the price of silk dropped dramatically.

Japanese military officers blamed the country's economic problems on corrupt politicians and believed that the only way to get the natural resources they needed was to take them by seizing other territories.

In 1931 the Japanese military control began to take control from the civilian government and establish a military government beginning the rise of Japanese Militarism.

Japanese Militarism combined a form of fascism with the ideologies of nationalism and imperialism. Emperor Hirohito remained the symbol of the state and the nation's ruler.

The Japanese army acted independently from the government and in September 1931,  led by General Tojo, invaded the resource-rich province of Manchuria in Northern China. The United States and Britain supported China against the actions of the Japanese.

To increase their power in Asia, and reduce their dependence on the west to obtain resources, the Japanese military looked towards Manchuria's iron and coal, Indochina's rubber, and China's vast range of natural resources.

July 1937 marked the beginning of total war between China, under Chiang Kai-shek, and Japan in the Second Sino-Japanese War. The Japanese defeated Chinese forces at Shanghai and seized Nanking in which an estimated 300,000 civilians were killed.

The ‘Rape of Nanking’ strengthened Anti-Japanese feeling in the United States which increased still further when the USS Panay, a U.S. gunboat, was sunk by Japanese aircraft in the Yangtze River outside Nanking on 12 December 1937.

The Japanese government made an apology which the US accepted as they did not want the sinking of the Panay to propel them into war - but the writing was on the wall and anti-Japanese feeling grew in the United States.

In response to the Japanese invasion of China, the sinking of the Panay and the German annexation of Austria Congress passed the Naval Act of 1938, known as the Second Vinson Act on May 17, 1938. The legislation "mandated a 20% increase in strength of the United States Navy". The purpose of the law was to triple the size of the US naval fleet by 1944.

On July 26, 1939, the US suddenly and dramatically took further action as Secretary of State Cordell Hull gave formal notice for termination of the 1911 Treaty of Commerce and Navigation with Japan in retaliation for its colonization of China. This action paved the way for the later trade embargoes which contributed to the Japanese decision to bomb Pearl Harbor

On September 3, 1939 WW2 broke out as Britain and France declared war on Germany. On September 5, 1939 the United States declared its neutrality in the war

With the outbreak of the war Germany began attacking British merchant ships as they transported goods from America to Britain. The British were forced to send warships from Southeast Asia to the Atlantic leaving the Pacific area vulnerable to attack.

In early 1940, the Japanese began to fortify the Marshall Islands located in the central Pacific between Hawaii and the Philippines posing a significant threat to American, British and Dutch colonial possessions in East Asia.

In June 1940 President Roosevelt ordered the US Pacific Fleet to move its main Pacific base from California to Pearl Harbor in the Hawaiian Islands as a deterrent to Japanese aggression. This action was not without significant risk because it placed the American Pacific fleet within striking distance of Japan's powerful navy.

The Japanese were a considerable military power. In 1940 the Japanese had 10 Aircraft Carriers in the Pacific compared to the US who had 3. The Japanese had 145 modern destroyers and  cruisers compared to the US who had 74.

President Roosevelt began to enforce economic policies to prevent further Japanese aggression in Southeast Asia introducing embargoes of steel and iron against Japan and restricting the sale of war materials. What is an embargo? An embargo is a government order to stop shipping goods into or out of a country.

In July 1940 Congress passed the Export Control Act to limit the exportation of material to Imperial Japan. The embargo halted the shipment of items including airplanes, machine tools and parts and aviation gasoline.

The Japanese were furious at the embargo. In September 1940, the Tripartite Pact was signed forming the Axis powers of Germany, Italy, and Japan, in which the three countries agreed to help each other if they were attacked by any additional power not yet at war with them. The intended target was the United States.

FDR believed that US entry into WW2 against Germany was inevitable but he hoped to avoid a war with Japan. The last thing he wanted was to be forced to fight on two fronts.

In April 1941, FDR extended lend-lease aid to China for their war against the Japanese (refer to the Lend-Lease Act ) hoping the Chinese would be able to distract the Japanese and prevent them from attacking elsewhere.

The US strategy failed and in July 1941 the Japanese military invaded and occupied Vietnam in southern Indochina. Southern Indochina derives from a combination of the names of "India" and "China", referring to the location of the territory between these two countries and included places such as Cambodia, Laos, Thailand and Malaysia and Vietnam.

Japanese occupation of Vietnam included the Cam Ranh naval base and eight airfields, just 800 miles from the Philippines, where Americans had troops. It also put Japanese airplanes in striking distance of the Dutch East Indies and also Malaysia, Hong Kong and Singapore which posed a direct threat to the British Empire and American interests in the area.

In July 1941 General Douglas MacArthur was recalled to active duty and named commander of U.S. Army forces in the Far East and was sent to the Philippines to build up American defenses in the Philippines. 

The United States reacted to the occupation of southern Indochina by following up its renouncement of the 1911 Treaty of Commerce with Japan and froze all Japanese assets in America, closed US ports to Japanese trade and placed an embargo on oil and gas

By freezing Japanese assets and Japanese bank accounts in America on July 26, 1941, Japanese citizens or businesses were unable to sell property they owned in the US or to withdraw money held in US banks.

The embargo on oil shipments to Japan was put into place on August 1, 1941. Oil was Japan's most crucial import, and more than 80% of Japan's oil at the time came from the US.

The Japanese ambassador to Washington held numerous meetings to resolve Japanese-American relations but FDR insisted that assets would only be released and the oil embargo would be lifted if Japan withdrew from Indochina and made peace with China.

A solution could not be found and the Japanese adopted a sense of urgency in its plans to dominate Eastern Asia and the Pacific. America’s 1938 Naval Act and additional plans to extend the US navy and air force meant the Japanese advantage would only last a couple of years until new US warships and warplanes came on line.

On November 3, 1941, the Japanese military presented a complete plan for the attack on Pearl Harbor to Emperor Hirohito. Emperor Hirohito approved the plan for a war against the United States, Great Britain and the Netherlands at the Imperial Conference on November 5, 1941. The war plan was scheduled to start at the beginning of December if an diplomatic settlement had not been achieved. All negotiations failed.

General Hideki Tojo, a hard-line militarist, was eager for war with America. The US Pacific Fleet based at Pearl Harbor in Hawaii posed the only significant threat to the aggressive territorial ambitions of the Japanese.

The Japanese government made the decision 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 was timed to coincide with Japanese attacks on the Philippines, British Malaya, Hong Kong and Thailand. Most of General MacArthur's aircraft in the Phillipines were destroyed on the same day.

On December 8, 1941 Britain and the United States declared war on Japan and America began its fight in WW2