Why did Japan Attack Pearl Harbor?

We discuss the events that led to the infamous Battle of Pearl Harbor, the event itself, and the aftermath.

pearl harbor-ship destroyed

On December 8, 1941, US President Franklin D. Roosevelt addressed the US Congress. He cited December 7, 1941, the date that Japan attacked Pearl Harbor, as a “date that will live in infamy.”

He was correct: That date has loomed large in the American consciousness every year since that time. Roosevelt’s speech was 7 minutes long, and 3 minutes later, the United States declared war on Japan.

The attack on Pearl Harbor was the decisive event that provoked the US into full-fledged participation in World War II, and the downfall of all the Axis powers. It had a devastating effect on Japan in particular, culminating in the atomic bombs on Hiroshima and Nagasaki.

So what made Japan employ such a provocative move? Why did Japan attack Pearl Harbor to begin with?


The USS Arizona Memorial, at Pearl Harbor in Honolulu, Hawaii.

Before the attack on Pearl Harbor

In the climate leading up to the attack, Japan was engaged in a military invasion of China with aspirations to conquer China and expand their empire into south Asia. Their plans for expansion and domination led them into eventual potential conflict with the United States and Europe, due to the Unites States’ presence in the Philippines, French and Dutch colonies in South Asia, and the UK’s holdings in China itself, including Hong Kong and Singapore.

As the European powers were weakened by war with Germany at home, Japanese forces wanted to expand into their colonies abroad. These Western colonies were also a vital supply chain for imports to reach China and support military resistance against Japan.

aircraft carrier docked in pearl-harbor

Aircraft carrier docked in modern-day Pearl Harbor

As a result of Japanese aggression in China and south Asia, trade sanctions were imposed, and the US ceased exporting oil to Japan. Japan needed to either face defeat and withdraw from China, or expand and conquer the oil-rich European colonies in south Asia. There was also internal tension between the imperial government, which was willing to make compromises in order to seek peace with the US, and the Japanese military, who were unwilling to make any withdrawal that might appear to be a sign of weakness.

As tensions in the area increased, the US moved a large percentage of the Pacific naval fleet from San Diego to Pearl Harbor, and built up the US military presence in the Philippines. Throughout 1941, the US and Japan were engaged in diplomatic negotiations, but relations steadily worsened.

Japan believed that any further military expansion into Asia would draw them into direct conflict with the US naval forces. They believed that a surprise attack would not only devastate the US Navy and render it ineffective in military action in the Pacific. They believed that the year or more that it would take for the US to re-establish naval strength in the Pacific would give them the time they needed to consolidate and strengthen their position. And they also believed that such an attack would devastate the morale of the United States, leading it to seek a compromise peace agreement favorable to Japan.

Attack on Pearl Harbor view from Japanese plane

View of the beginning of the attack from a Japanese plane

The attack itself

In the attack on Pearl Harbor, Japan chose to mount a swift, surgical attack. They focused on battleships, since they believed that battleships would be crucial to any effective naval military force. They knew that America’s three Pacific aircraft carriers would not be in Pearl Harbor at the time, but did not believe that aircraft carriers would be decisive in a victory. The decision to bomb Pearl Harbor was intended to destroy or cripple as many US battleships as possible.

In addition to the absence of the aircraft carriers, the Japanese plan also had another unavoidable flaw in that the ships would be docked in shallow waters on military bases. This meant that crew casualties would be lower, because many of the crew would naturally be on shore, not on alert for an attack, and that sunk or damaged ships would be more easily salvaged and repaired.

During the attack on Pearl Harbor, Japan did not bomb other naval targets like the submarine base, oil tanks, or the navy yard. They did not believe these facilities would be as important as they actually turned out to be.

USS West Virginia sinking at Pearl Harbor

USS West Virginia sinking at Pearl Harbor

During the Battle of Pearl Harbor

Admiral Yamamoto intended for the attack to commence thirty minutes after Japan had notified the US that peace negotiations were ended. They accordingly transmitted a message to the Japanese Embassy in Washington, DC, but the message was not transcribed or presented until an hour after the attack began. Historians feel that, in any case, the wording of the message would not have been interpreted as a declaration of war.

The attack began at 7:48 a.m., and Japan won decisively. They sank 4 battleships, destroyed 188 aircraft, and killed 2,335 military personnel. In addition, they damaged 4 battleships, 3 cruisers, 3 destroyers, 159 aircraft, and injured another 1,143 military personnel. 68 civilians and 3 civilian aircraft were also lost. In the battle, Japan lost just 4 midget submarines, 29 aircraft, and 64 soldiers.

Simultaneously with the attack on Pearl Harbor, Japan had also mounted attacks on targets in the Philippines, Guam, and British Hong Kong and Singapore.

Franklin Roosevelt signing declaration of war against Japan

President Franklin Roosevelt signing declaration of war against Japan

Consequences of the attack on Pearl Harbor

Partly due to the simultaneous attacks on English colonial holdings, and partly due to Winston Churchill’s vow to declare war on Japan “within the hour” of an attack on the US, the United Kingdom declared war on Japan. In fact, that declaration was made even before the United States’ own declaration of war against Japan on Dec 8. On December 11, Germany and Italy in turn declared war on the United States, and the US was suddenly, completely engaged in WWII.

Another notable consequence of the Japanese attack on Pearl Harbor was the widespread internment of Japanese Americans on the west coast of the United States.

Finally, either due to the changing nature of naval strategy, or due to the adaptation required by the attack on Pearl Harbor, the US was victorious in the Pacific not due to the presence of battleships, but due to the combination of submarines and aircraft carriers. The essential infrastructure needed for effective naval presence in the Pacific was not lost during Pearl Harbor. Instead of defeating the US navy and devastating American morale, the attack on Pearl Harbor pushed a reluctant America into military action.

We’ve got lots more like this here at Why not learn about the Declaration of Independence next?

We’ve also got a great history piece on The Great Wall of China.

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Extra image sources:

By Imperial Japanese Navy – Official U.S. Navy photograph NH 50930., Public Domain

By U.S. Navy, Office of Public Relations [Public domain], via Wikimedia Commons

By National Archives and Records Administration:, Public Domain

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