US Freezes Japanese Assets — Oil Embargo Cuts 80% of Japan's Supply

President Roosevelt froze Japanese assets in the United States on July 26, 1941, following Japan's occupation of southern Indochina. The British Empire and Netherlands East Indies followed suit, effectively cutting off 80% of Japan's imported oil and 75% of its trade. Japan's military planners calculated their oil reserves would last roughly 18 months, after which the navy would be immobilized. The embargo was the decisive trigger for Japan's decision to attack Pearl Harbor and seize the oil-rich Dutch East Indies — accepting war with the US rather than submit to Western demands to withdraw from China.