Yeah, the USA could definitely have defeated Japan on its own. Matter of fact, Admiral Yamamoto was of that opinion also, and he was supreme commander of the Japanese Navy. He did not think Japan could win a war with the USA...

But the Japanese Army was running tbe government. So Yamamoto, when given the order by the Army chiefs, had to do his duty like a good Japanese and plan to fight a war he didn't believe he could win.

The Pearl Harbour attack was Yamamoto's plan to better the Japanese chances in that war. It was very imaginative, and it was carried out with great skill and panache, but I believe in retrospect that it was about the most self-defeating thing the Japanese could have come up with, as I mentioned in an earlier post. It just made things worse for them in the long run.