Question

What caused U.S./Japanese tension prior to the attack at Pearl Harbor?

Answer 1

The attack on Pearl Harbor was due to a series of events but the real reason was the 1931 invasion of Manchuria by Japan.  Japan expanded slowly into China, leading to the Second Sino-Japanese war in 1937. During 1940 Japan invaded French Indochina in an move to embargo all imports into China which also included war supplies procured from the U.S. This  prompted the United States to embargo all oil export  in association with the British and the Dutch was a big setback   for Japan, which imported 90% of its oil. Without oil Japan’s military could not function and all war efforts would fall apart. Negotiations had been going on for months between Washington and Tokyo, without any resolution, so Japan decided to attack first.