Not Verified, But...

In June 1941 Japan occupies French Indochina to cut the Chinese supply routes, todays Laos Cambodia and Vietnam which the US has said will result in an oil and raw materials embargo. The US is Japan's biggest source of oil, we are the worlds largest oil exporter in 1941! To Japan this sanction is the final straw and she begins war planning to start the war after the fall rice harvest is done in November-December 1941. The US moves the fleet from San Diego to Pearl Harbor.