If Japan had either listened to Yamamoto’s advice not to attack the U.S., or had carried out his actual plan in its entirety, world history would have been very different:
Yamamoto proposed not merely destroying the U.S. fleet, but landing Japanese marines in Hawaii in sufficient force to seize control. The U.S. would have been left with San Francisco as its nearest deep water port to the Japanese home islands, and Japan would have had a forward position in which to base aircraft to harass the U.S. fleet. Fortunately, Yamamoto was not regarded as sufficiently “bushido” and his plan was watered down by folks more in the favor of Tojo and the Emperor.
Do you have a citation for that? Never heard that claim made before. Oahu was a fair sized island. It took a division of US Marines to seize a toehold on Guadalcanal. I imagine it would have taken a multi-division force to take Oahu. Slow transports would have made the surprise carrier strike far more difficult as they would have cruised separately.
Yamamoto may have proposed the Hawaii invasion as a deal-breaker to make Tojo and company realize the enormity of the war they were entering upon and the impossibility of ultimate success. If so, it was ignored.