Yamamoto and the Navy were strongly against going to war against the US, but the admirals knew there was a good chance they would be assassinated if they didn't go along. Japanese politics weren't very civilized in that era.
Thank you for that correction. Now that I think of it, after the one or two bombs were dropped - did the Emperor want to surrender, but the military tried to do a coup? I seem to recall a movie about that, and the government was able to get the surrender message out on the radio just moments before the military arrived??
From the web (AI):
A group of Japanese junior military officers, led by Major Kenji Hatanaka, attempted a coup on the night of August 14–15, 1945, to prevent Emperor Hirohito’s pre-recorded surrender speech from being broadcast. Known as the Kyūjō Incident (or Imperial Palace Incident), the plotters seized the palace, killed the commander of the Imperial Guard Regiment, and tried to destroy the recording. However, they failed to find the recording and secure the Emperor’s person, and the speech was broadcast as planned, leading to Japan’s formal surrender and the end of World War II.