Skip over navigation

World War II (1939–1945)

History SparkNotes

Japan and Pearl Harbor

The Invasion of Russia

The Nazis’ “Final Solution”

1937 Japan goes to war with China
July 1939 Roosevelt announces that Treaty of Commerce and Navigation will not be renewed
July 2, 1940 U.S. Congress passes Export Control Act
August Japan declares greater East Asia co-prosperity sphere
September 27 Japan signs Tripartite Pact with Germany and Italy
January 1941 Yamamoto prepares plan for attack on Pearl Harbor
July Japanese troops occupy Indochina
October Hirohito gives general approval for Pearl Harbor attack
November 8 Hirohito approves formal battle plan for attack in December
November 26 Japanese attack fleet sets sail from Japan
December 7 Japan launches surprise attack on Pearl Harbor
December 8 United States and Britain declare war on Japan
December 11 Germany declares war on United States
Key People
Franklin D. Roosevelt -  32nd U.S. president; implemented economic penalties that angered Japan; requested war declaration after Japanese attacked Pearl Harbor in December 1941
Yamamoto Isoroku -  Japanese admiral who planned surprise attack at Pearl Harbor
Hirohito -  Japanese emperor; approved Pearl Harbor attack plan
Richmond K. Turner -  U.S. Navy admiral; warned that navy be put on high alert status and security increased at Pearl Harbor, but recommendations were implemented only partly

Tensions in the Pacific

In the years prior to the outbreak of World War II in Europe, tensions were also escalating in the Pacific region. Japan, which had been at war with China since 1937, had declared openly its intent to take over as much of eastern Asia as it could. It also had serious ambitions toward taking territory in the Soviet Union. If Germany, which the Japanese government saw as a potential ally, would attack Russia from the west, Japanese military leaders felt that they stood a good chance of seizing Soviet-controlled territory in the east. The signing of the German-Soviet Nonaggression Pact in 1939 therefore caused a huge scandal in Japan, as it directly undermined Japan’s plans.

Japan and the United States

In the meantime, the United States was becoming more and more of a problem for Japan. Throughout the 1930s, the United States and many European nations, suffering from the Great Depression, enacted high protective tariffs. These tariffs greatly curbed Japanese exports and heightened the effects of their own economic depression. The poor economic conditions caused strong anti-Western sentiment in Japan and were a strong factor in forcing the Japanese invasion of China.

In July 1939, President Franklin D. Roosevelt decided not to renew the 1911 U.S.-Japan Treaty of Commerce and Navigation, which was due to expire in January 1940. Then, on July 2, 1940, the U.S. Congress passed the Export Control Act. Together, these two actions effectively eliminated Japan’s primary source of oil, scrap metal, and other material resources needed for war.

These developments dealt not only a severe economic blow to Japan but also a humiliating slap in the face to Japan’s leaders, who felt that the United States had no right to pass judgment on them or to interfere in their affairs. Although Japan was still smarting from the German-Soviet Nonaggression Pact, the United States’ actions were enough to overcome this resentment, and on September 27, 1940, Japan signed the Tripartite Pact with Germany and Italy. The pact made the three nations official allies.

The United States Prepares for War

Although the United States remained officially neutral during the first two years of World War II, the Roosevelt administration was far from indifferent or oblivious to the conflict. The United States provided material support first to Britain and later to the Soviet Union, secretly at first but then with increasing openness over time. Chief among these measures was the March 1941 Lend-Lease Act, which empowered Roosevelt to give aid to the Allies in exchange for whatever kind of compensation or benefit the president deemed acceptable. The American people also paid close attention to the events developing in the Pacific and, by mid-1941, considered war with both Japan and Germany to be likely possibilities.

U.S. intelligence services had direct access to Japanese coded transmissions, so U.S. officials were well aware that the Japanese were planning something against them—they just did not know precisely what. One man in particular, Admiral Richmond K. Turner, strongly urged that U.S. forces be placed on a higher state of alert, as he was particularly concerned about the U.S. Navy base at Pearl Harbor, Hawaii. During previous U.S. war games and exercises, Pearl Harbor had proven highly vulnerable to surprise attacks. Although Turner’s advice was considered, only some of his recommendations were implemented.


Indochina was a French-administered colony in Southeast Asia comprising the present-day nations Vietnam, Laos, and Cambodia. On July 20, 1941, Japanese troops entered the region and quickly occupied the entire area. Japan justified the occupation as necessary in order to deny resources to the Chinese resistance. However, Indochina also provided Japan with a convenient base for launching attacks against other countries and territories in the region, including Singapore and the Dutch East Indies. Both the United States and Britain saw this move as a threat and a clear indication of Japan’s intention to continue its expansion throughout the Pacific Rim. The two countries expressed their disapproval by freezing Japanese bank accounts.

The Japanese Attack Plan

As early as January 1941, Admiral Yamamoto Isoroku developed a plan for attacking the U.S. fleet at Pearl Harbor and carried out training exercises to prepare specifically for such an attack. In October, the Japanese emperor, Hirohito, gave his general approval for action against the United States and, on November 8, approved the specific Pearl Harbor attack plan.

On November 2526, the Japanese fleet set sail from Japan, unseen by U.S. spies. Even then, however, some Japanese officials disapproved of the plan, and it continued to be debated heatedly. By December 1, all discussion had ended, and Hirohito ordered the plan to proceed. Japan’s goal was to make a permanent end to Western interference in its affairs by obliterating the U.S. and British military capabilities in the Pacific.

Pearl Harbor

On the morning of December 7, 1941, a fleet of six aircraft carriers, twenty-five submarines, and nearly three dozen additional support ships was sitting 200 miles north of the Hawaiian island of Oahu—in the open sea, far beyond the line of sight of any U.S. forces. The first wave of Japanese planes numbered more than 180. Although U.S. radar operators saw the massive formation nearly a full hour before the attack began, they raised no alarm, because they mistook the planes for a group of U.S. bombers expected to arrive from California around the same time. This mistake happened in spite of the fact that the planes seen on the radar were coming from the wrong direction and were much more numerous than the expected bomber fleet.

The first wave arrived at the U.S. Navy base at Pearl Harbor at 7:55 a.m. and achieved complete surprise; only nine Japanese planes were lost. The primary targets were major U.S. warships, most of which were docked close together in neat lines. These included eight of the nine battleships in the U.S. Pacific Fleet, along with several dozen other warships. The Japanese also targeted six nearby military airfields. A second attack wave of more than 160 planes followed just over an hour later. By this time, the Americans were well alerted and managed to bring down twenty Japanese planes.

In all, the attack on Pearl Harbor killed 2,402 Americans, destroyed five battleships completely, put three more out of commission, sank or seriously damaged at least eleven other warships, and destroyed nearly more than 180 aircraft on the ground. The only good luck the U.S. Navy had was that none of its aircraft carriers were in port at the time and that the Japanese bombers failed to hit the large fuel reserves in the area.

In addition to attacking Pearl Harbor that day, Japan also attacked the U.S. territories of Guam, the Philippines, Wake Island, and Midway Island, as well as British interests in Malaya and Hong Kong.

Declarations of War

The next day, December 8, Roosevelt went before both houses of the U.S. Congress to request a declaration of war against Japan; after a vote, the declaration was formalized just hours later. Britain declared war on Japan on the same day. Three days later, on December 11, Germany declared war on the United States. Thus, the United States was now at war with both Japan and Germany and able to enter fully into its alliance with Britain.

Reaction in the United States

The story of the attack on Pearl Harbor has become a part of American culture. For the American population, the event was a traumatic shock, as few regular Americans knew much about the events in Japan leading up to the war or about the level of hostility that Japan bore toward the United States. Officials in the U.S. government, however, could not claim such obliviousness. Uncomfortable questions were soon raised in Congress and on the streets about why the United States had been so poorly prepared and why the U.S. intelligence services had failed to see the attack coming or raise warnings earlier.

Over the years, historical analysis has shown that there were many warning signs in the months before the attack and that some U.S. military leaders, most notably Admiral Turner, had been concerned that the Pearl Harbor base was particularly vulnerable to attack. Furthermore, the United States was able to decode and read Japanese military communications until shortly before the attack, when Japan abruptly changed its military codes. By the evening of December 6, 1941, U.S. military and government officials, including President Roosevelt, were certain that Japan was planning a major action against U.S. interests. A meeting was even scheduled for 3:00 p.m. on December 7 to discuss the matter. Unfortunately, the target of the attack was unknown, and no one at Pearl Harbor was notified to be on alert.

To this day, there is avid speculation about how much the United States could and should have done to prevent the attack, and even more speculation over how much the United States and its allies knew about Japanese plans. Britain’s prime minister, Winston Churchill, was desperate for active U.S. participation and had long been pressing his old friend Roosevelt to enter the war. Some historians maintain that British intelligence had specific information about the Pearl Harbor attack and that Churchill deliberately kept the information to himself so that the United States would finally go to war. These claims, however, remain unconfirmed.

More Help

Previous Next

Follow Us