The Japanese Empire, under the rule of Emperor Hirohito, in order to manage to continue with the expansion and gain new territories, needed much more oil than what its supplies where.
The need for oil meant that Japan will attack the places in the region where there are solid amounts of oil reserves, and they did. They attacked and conquered parts of Southeast Asia, and got hold onto the large oil reserves that they desperately needed for their military machinery.
Soldiers were drilled in infantry tactics, usually based upon a manual written before the war by West Point professor William J. Hardee (Rifle and Light Infantry Tactics: for the Instruction, Exercise and Maneuver of Riflemen and Light Infantry, published in 1855).
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