Why did Japanese leaders believe an attack on the U.S. Pacific Fleet would help them conquer Southeast Asia?

Japanese leaders believed that a surprise attack on the U.S. Pacific Fleet at Pearl Harbor was essential to their broader strategic goals in Southeast Asia. Following the United States' decision to freeze Japanese assets and impose a total embargo on oil shipments in 1941, Japan faced a critical shortage of petroleum and other vital resources necessary to sustain its military and industrial efforts.123

Japanese military planners concluded that they needed to seize the oil-rich Dutch East Indies to achieve self-sufficiency. However, they feared that the U.S. Pacific Fleet would intervene to stop this southward expansion. By launching a preemptive, crushing blow against the U.S. fleet at Pearl Harbor, Japanese leaders, most notably Admiral Yamamoto Isoroku, intended to eliminate the threat of a flank attack. They believed this would clear the way for the unhindered conquest of Southeast Asia and the Indonesian archipelago, allowing Japan to establish its desired economic bloc, the Greater East Asia Co-Prosperity Sphere.24516