The Real Story
Why it happened?
The differences between China and Japan started driving the U.S. and Japan away and the U.S. was getting really angry because they thought that by the time Japan was done they would've taken over most of China.
Who was responsible for it?
Isoroku Yamamoto was the one who came up with the plan to go drop atomic bombs on a Sunday because he said that it would take everyone by surprise and they wouldn't react fast enough.
What did the Japanese want to gain out of it?
They wanted to have their own places where they can get their own resources from the places that they have gained. They also felt as if the president of the U.S. Franklin D. Roosevelt was pushing them to a corner and they wouldn't be able to get any of their resources.