Some say the roots of the European war were laid in the shambles at the end of WWI, or even say that it goes back to Bismarck, and that the Pacific side goes all the way back to the Meiji days for the Japanese aggression.

I think the origins of the war came in 2 parts -- Pacific and European, and only merged when the US entered the war. Of course, at the same time the US was attacked, so were the British and the Dutch in the Pacific. At the time the US was already involved in supplying belligerents in Europe, and had been building to a confrontation with Japan for a while. However, until that time, the only linkage between Japan's war and Germany's war was that the US was giving some supply to opponents of both aggressors, meaning China and Britain.

(Yes, I'm aware that the Japanese and Russians had clashed at the Manchurian border a few times, but, the Japanese had decided that dog wasn't going to hunt, and had made a non-aggression pact with the Soviet Union)