What causes a nation to attack an unsuspecting naval base filled with men simply going about their day? How do the leaders of a country justify the killing of thousands, in a nation it’s not even at war with? These are questions that many people pose when they look at the surprise attack on Pearl Harbor on December 7th, 1941.

To know why Japan sent an attack group to cripple the United States Navy, it helps to look back through the months leading up to that day of infamy.

Joining the Axis Powers

Signing of the Tripartite Pact. Seated from left to right: Saburō Kurusu (Japan), Galeazzo Ciano (Italy) and Adolf Hitler (Germany).

Japanese troops didn’t join the fight in Europe, but Japan did have a pact with Germany and Italy. Signed on September 27th, 1940, the Tripartite Pact bound the three nations together in a mutual defense agreement, mainly against the United States. It’s believed that Japan signed it as a means of keeping US forces from joining the Allies.

 

 

The Trade Embargo

Considered one of the major reasons Japan went after the United States, the trade embargo ceased delivery of oil and other important resources necessary for war, which of course infuriated Japan’s leaders. Displeased with the aggression the Japanese had been showing in Asia and the Pacific, the United States joined the United Kingdom in cutting off Japan’s supply of oil and froze its assets within the US.

Japan’s March Through Asia

By 1939, Japan had shown that it was able to rip through Asia, and desired to continue to do so without involvement from an outside power. Knowing that the United States could pose a military threat in the expansion throughout Asia and the Pacific

Admiral Isoroku Yamamoto Planned Attacks

Admiral Isoroku Yamamoto

islands, Japan started to ponder a preemptive strike against the United States.

In August of 1939, Admiral Isoroku Yamamoto, the mind behind the Pearl Harbor attack, took command of Japan’s Combined Fleet.

Signs of Aggression

In early 1941, Yamamoto approached other officers about an attack on Pearl Harbor and, within a month, the United States received a warning from Joseph Grew, theAmerican ambassador to Japan, that an attack on Pearl Harbor was being planned. Since American military experts believed Japan would strike Manila, in the Philippines, his warning was ignored.

By July of 1941, Yamamoto finalized the plan to attack Pearl Harbor and began training his fleet. Two months later, American intelligence intercepted and decoded a message between Japanese naval intelligence and Japan’s Consul General in Honolulu, requesting the location of the battleships at Pearl Harbor. The intercepted message was ignored.

The Last Straw

A month prior to the attack, Japan sent a diplomat to Washington to negotiate the nation’s expansion in Asia. If the United States refused to accept this aggression, Japan was well-prepared to launch the surprise attack.

By 0755 on December 7, 1941, the first wave of Japanese fighters launched the assault. For approximately two hours, Japan bombarded Pearl Harbor in hopes of crippling the US Navy.

Cause and Effect

With over 2,400 Americans killed at Pearl Harbor, the nation regrouped and declared war on Japan the very next day in a near-unanimous vote in Congress. Despite Japan’s efforts to destroy the American fleet, most of the battleships returned to service and went on to play vital roles in major battles in the Pacific Theater.

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