[Sherman Logan]

Lastly, Stalin knew by then that the danger posed by Japan in the Far East had passed when Japan "Struck South" after Pearl Harbor.

Few Americans know that a major reason Japan chose to attack Pearl is that they had the absolute crap kicked out of them in 1939 by the Red Army in Manchuria. Zhukov, who we would hear from again, forced them to fight a stand-up mechanized warfare battle and destroyed something like 3/4 of the Japanese force.

The Japs decided they maybe didn't want to conquer Siberia after all and went with the alternative "Strike South" strategy of the Navy, which, at least in the Jap strategists' minds, required taking out the US Pacific Fleet.

Thus Pearl Harbor.

[Tallguy]

Put simply, the Japanese Army wanted to focus operations in Manchuria and Northern China. The Japanese Navy, mindful of the need for ready access to petroleum products, wanted to take the Dutch oil fields in the Dutch East Indies (Germany was occupying Holland, so these colonies were ripe for the taking. Same went for French Indochina). Japan chose to "Strike South" as the easy targets were there, and, more importantly, the Japanese Army was politically discredited by their defeat at the hands of the Soviets in Mongolia.

Due to the US Oil Embargo, the Japanese Navy only had reserves enough for 6 months to a year of combat operations had they not seized the Dutch oil fields (& returned them to operation). Thus the entire IJN might have been literally tied up at the piers if the "Strike South" stategy had not succeeded in gaining approval.