Events leading to the attack on Pearl
Harbor
A series of historical events leading to the
attack on Pearl Harbor occurred that con-
tributed to the actual attack. War between
Japan and the United States had been a pos-
sibility that each nation’s militaries planned
for since the 1920s, though real tension did
not begin until the 1931 invasion of Man-
churia by Japan. Over the next decade, Japan
expanded slowly into China leading to all out
war between the two in 1937. In 1940 Japan
invaded French Indochina in an effort to em-
bargo all imports into China, including war
supplies purchased from the US. This move
prompted the Imperial Japanese Navy to es-
timate that it had less than two years of
bunker oil remaining and to support the ex-
isting plans to seize oil resources in the
Dutch East Indies. Planning had been under-
way for some time on an attack on the
"Southern Resource Area" to add it to the
Greater East Asia Co-Prosperity Sphere
Japan envisioned in the Pacific.
The Philippine islands, at that time an
American territory, was also a target of
Japan’s. The Japanese military concluded that
an invasion of the Philippines would provoke
an American military response. Rather than
seize and fortify the islands, and wait for the
inevitible US counterattack, Japan’s miltary
leaders instead decided on the pre-emptive
Pear Harbor attack, which would negate the
American forces needed for the liberation
and reconquest of the islands. Such an attack
would certainly provoke American military in-
volvement in the war. This would complicate
matters for the Japanese and a preventive
strike was planned which resulted in the at-
tack. Planning for an attack on Pearl Harbor
had begun in very early 1941, by Admiral
Isoroku Yamamoto. He finally won assent
from the Naval High Command by, among
other things, threatening to resign. The at-
tack was approved in the summer at an Im-
perial Conference and again at a second Con-
ference in the fall. Over the next year, pilots
were trained, and ships prepared for its exe-
cution. Autho