I agree. There are oil fields in eastern Russia but they weren't well developed then. They would have never been able to sustain an occupation of the territory in the USSR while holding the rest of their gains in China and SW Asia against the Allies. Maybe the US may have just entered the war on its own at that point. Roosevelt was certainly convinced that war was on the way, and prepared as well as he could for it. Pearl Harbor was basically a gift to the US government for public support against Japan.