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Billy Mitchell predicted Japan would attack back the 20s

Don't forget that not only did he predict Japan would attack the United States in 1925 with mention of Pearl Harbor, but it was part of a 325 page report. It wasn't some off-hand remark - Mitchell made a clear and detailed case that Japan was going to attack and that carriers were going to play a major role.

There were missteps on both sides - Japan believed that attacking British colonies would bring the US into the war, and they believed they HAD to attack the US first because of that. Had they know that the US would allow some British colonies to be lost, it might have changed things. FDR believed that reinforcing the Philippines would make Japan think twice about further invasions.

In addition to Billy Mitchell predicting war in the 1920s, there was a group within the US military preparing for war with Japan. The "Orange" war plan started to be formulated in either 1918 or 1919, and the people involved with designing it were discussing war with Japan in 1905 and how to get ships to the Pacific from the Atlantic quickly. An Admiral Rogers laid out plans in 1911 that ended up being used in the 1940s.

People on both sides knew war was going to happen.