Why Did Japan Attack Pearl Harbor in 1941?

On December 7, 1941, Japan launched a surprise attack on Pearl Harbor, the base of the U.S. Pacific Fleet. This was not a mere military provocation but a result of Japan’s strategic decision made under desperate circumstances. Ironically, Japan believed this attack would allow them to avoid war with the United States. How could such a paradoxical decision have been made?

America’s Reluctance to Enter the War

After World War I and during World War II, the U.S. profited from selling military supplies while avoiding direct involvement in conflicts. Even when Germany attacked a U.S. warship in September 1941, the U.S. refrained from declaring war, showing its strong aversion to entering the conflict. The U.S. was determined to stay out of World War II.

Yet, Japan, which could have stayed under the radar, deliberately provoked the U.S. in December 1941. In this article, we will explore the reasons and thought processes behind Japan’s decision to wage war against the U.S.

Japan’s Expansionism

In the 1930s, Japan aggressively expanded its territory in East and Southeast Asia:

• 1931: Japan instigated the Manchurian Incident and established the puppet state of Manchukuo.
• 1937: The Second Sino-Japanese War began, with Japan occupying major Chinese cities like Beijing and Shanghai.
• 1940: After France surrendered to Germany, Japan moved into French Indochina (Vietnam).

During this period, European nations, weakened by World War I and the Great Depression, were unable to curb Japan’s expansion. By June 1940, France was effectively erased from the European map by Nazi Germany, leaving its colonies vulnerable. Japan seized this opportunity, signing the Tripartite Pact with Germany and Italy on September 27, 1940, forming the Axis alliance.

Shortly after, in July 1941, Japan began occupying French Indochina. This move alarmed the U.S., which had adopted a strategy of maintaining dominance over the Pacific and Atlantic Oceans. The U.S. viewed Japan’s expansion into Indochina—close to the Philippines, a U.S. territory—as a direct threat to its Pacific influence. Consequently, the U.S. decided to take action to curb Japan’s ambitions, even at the cost of reduced export revenues.

The U.S. Oil Embargo on Japan

Japan’s situation was dire. Engaged in a total war to conquer China, Japan required vast amounts of oil and coal to sustain its military operations. However, the U.S. imposed an oil embargo, froze Japanese assets in the U.S., and halted the supply of critical resources like oil and steel:

• July 1941: Japanese assets in the U.S. were frozen.
• August 1, 1941: The U.S. banned oil exports to Japan.

For Japan, which had no domestic oil production, this was a devastating blow. Tanks, fighter planes, and other military equipment relied heavily on oil and steel, both of which were now cut off. Japan attempted to resolve the issue diplomatically through its ambassador in Washington, but negotiations faltered due to Japan’s uncompromising stance.

Japan’s Desperate Choice

The U.S. demanded that Japan retain only Manchuria and withdraw from China and Southeast Asia. However, Japan’s military insisted on dominating all of China, leading to a complete breakdown in negotiations.

Japan was also reeling from the effects of the Great Depression, with its economy in shambles. In 1932, a military coup led to the assassination of Prime Minister Tsuyoshi Inukai, leaving Japan with little room to retreat. The Japanese government, fueled by militarism, had convinced its people that conquering China would solve all their problems. The nation was intoxicated by the illusion that controlling the Chinese mainland would bring prosperity. With public attention fixated on the war and territorial expansion, Japan could not accept the U.S.’s demands to limit its ambitions to Manchuria.

The Pearl Harbor Attack

Japan devised a bold plan, banking on two key assumptions:

1. The U.S. did not want war: Isolationist sentiment was strong in the U.S., and President Roosevelt had publicly declared neutrality.
2. A decisive strike could break U.S. resolve: By crippling the U.S. Pacific Fleet at Pearl Harbor, Japan believed it could force the U.S. to negotiate.

In a paradoxical move, Japan decided to “start a war to avoid a war.” On December 7, 1941, Japan deployed six aircraft carriers, 16 destroyers, and 353 aircraft to launch a surprise attack on Pearl Harbor, devastating the U.S. Pacific Fleet in half a day.

Casualties and Damage

• U.S.: 9 battleships sunk, 188 aircraft destroyed, 2,404 personnel killed.
• Japan: 4 battleships sunk, 29 aircraft lost, 100 personnel killed.

Japan then swiftly occupied U.S.-controlled territories like the Philippines, Malaysia, and Indonesia, expecting the U.S. to acquiesce and seek peace talks.

U.S. Declaration of War

Contrary to Japan’s expectations, the Pearl Harbor attack enraged the American public, who had previously opposed entering the war. The audacity of Japan’s attack united Americans in demanding retribution. On December 8, 1941—the day after the attack—the U.S. officially declared war, entering World War II.

Japan’s assumption that the U.S. would avoid war proved to be a catastrophic miscalculation.

U.S. Mobilization

Following the attack, the U.S. ramped up its war machine, with shipyards operating at full capacity to produce massive quantities of ships and military supplies. Between 1942 and 1945, the U.S. spent over $5 trillion on the war effort. By 1942, Germany and Italy began to weaken in Europe, culminating in Germany’s surrender on May 8, 1945.