The original plan was defeat Germany and Italy first and then defeat Japan. But we were able to take the war to Japan right away with leftovers from Europe and a Navy that would not be needed to defeat the Axis. On the cheap for us.
By 1945 we had more than 12 million men and women under arms and almost all that would have been directed at Japan after Germany's surrender had the bombs not ended the war. And they never even put soldiers on the ground in Hawaii, much less the US mainland. All Yamamoto's fears were right.
True, but it's also important to keep in mind that following the Battle of the Santa Cruz Islands, the US was down to
ONE functioning carrier in the Pacific, the USS Enterprise, and it was significantly damaged: A remarkable repair job while underway (returning to the Solomon Islands) allowed it to stay in action. Fortunately, the Japanese Navy had been severely degraded as well.
http://en.wikipedia.org/wiki/USS_Enterprise_(CV-6)