Why did Japan attack Pearl Harbor on December 7, 1941?

Japan attacked Pearl Harbor on December 7, 1941, primarily to neutralize the U.S. Pacific Fleet, which Japanese strategists believed was the main obstacle to their planned conquest of Southeast Asia and the Indonesian archipelago.12

This decision was driven by several escalating factors:

• Economic Embargoes: Following Japan’s occupation of Indochina in 1941, the United States severed commercial and financial relations, froze Japanese assets, and imposed a total embargo on petroleum and other vital war materials. Japan, lacking sufficient stockpiles, viewed this as a critical threat to its industrial economy and military capacity.234
• Strategic Ambition: Japan sought to establish the Greater East Asia Co-Prosperity Sphere, a self-sufficient economic bloc under its control. By seizing resource-rich colonies held by Western powers, Japan aimed to become the dominant power in the Pacific.35
• Diplomatic Failure: Negotiations between the U.S. and Japan throughout 1941 failed to reach an agreement. The U.S. demanded that Japan withdraw from China and Indochina, terms the Japanese government refused to accept.234

Admiral Yamamoto Isoroku orchestrated the attack, believing that a decisive strike would allow Japan to "run wild" and secure its defensive perimeter before the U.S. could effectively respond.63