The most likely point of divergence is the Battle Of Midway, in which the Japanese win the battle instead of the Americans, leaving a section of the Pacific open for Japanese ships to stroll through to Hawaii for a full scale invasion and if that were to occur then an attack or possible invasion of the West Coast of the United States and more of a focus on the Aleutian islands. This P.O.D could only occur if Isoroku Yamamoto, Nobutake Kondo and Chuichi Nagumo made a more competent and carefully thought out plan and the Japanese message code JN-25b weren't partially broke among countless other things that brought their defeat in the battle and turned the tides in the American's favor.
Thoughts?