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As you can read in the first 3 paragraphs of the following Wikipedia link about the causes that led to the Japanese attack on Pearl Harbor. Japan, that had already invaded China which was a U.S. ally, invaded in 1940 what was then the French Indochina (yellow circle). The French Indochina was approximately located in the region occupied today by Vietnam and Laos.
To retaliate, the United States imposed a restriction on oil sales to Japan, which is one of the poorest countries in the world in terms of oil reserves, and even today it imports almost all of the oil it consumes. At that time Japan’s was importing most of its oil from the U.S., since most of the today’s big Middle East oil fields had not been discovered yet. For example the first significant oil filed in Saudi Arabia was discovered in 1938.
According to Wikipedia, the Japanese estimated that because of the American embargo on oil exports to Japan, they could not achieve oil sufficiency for their navy for more than 2 years, something that enhanced their plans of invading the oil rich Dutch East Indies (blue circle), which is today’s Indonesia, and to also invade the Philippines, which at the time was an American territory. Even today, Indonesia is the 30th richest country in the world, in terms of oil reserves, but at the time she was much richer since most of today’s known reserves had not been discovered yet.
However the Japanese knew that the Americans would retaliate if they were to invade Indonesia and Philippines, and they decided that destroying their Pacific Ocean fleet would be the right strategy. On December 8 1941, 353 Japanese aircrafts attacked Pearl Harbor and destroyed all 8 American battleships, another 8 ships of the American Navy, and a total of 188 American military aircrafts, leaving behind 2.400 dead and 1.180 wounded Americans.
For the Pearl Harbor attack see