If they had attacked China instead of the US, then history would be different.
The US would not have gotten involved until Japan had solidified itself in the Pacific. The nazis would have completely overtaken Europe.
That was the single biggest mistake of the war. Should not have given the US any reason to be involved. Our economy was still devastated from the Great Depression. US morale was at an all time low.
My guess is that they thought the US was so far down that we were going to fold with a little show of force.
Wonder who spearheaded the idea that Pearl Harbor was a great idea to vanquish the US?