the world looked down on japan at this point in time. and Japan capitalized on this fact. they built some of the largest warships in history, as well as challenging America, and bleeding America for every island they fought upon. being underestimated costs millions of lives on both sides.
Point of fact, this isn't quite true. While plenty of analysts and strategists underestimated the Japanese, it wasn't quite out of racism or arrogance; rather, it was Japan initiating strict information control and and having geographical isolation on its side. Considering that the Zero didn't come into service until something like 1940, and two of Japan's six pre-war fleet carriers were commissioned not long before the war, and that
no one had any idea that Japanese carrier doctrine/tactics had become so advanced and practiced, it's pretty understandable. Even the attack on Pearl Harbor was done at the very edge of Japan's logistical reach, with all of Japan's fleet carriers, in an attack that was practiced and planned for months.
It's relatively understandable that everyone was caught by surprise at Japan's sudden, elaborately planned, well-prepared, and large-scale offensive across the Pacific, because the only fighting Japan had been doing was in China and the border with Russia--and considering that Japan was in a bitter slog against the Chinese (who were even dealing with a civil war of their own at the time) and had gotten its butt kicked by Russia, it was very surprising that Japan was suddenly
very competent and prepared for such an ambitious, wide-spread undertaking. Of course, it all played to Japan's strengths--it was at a time when Japan had recently introduced an extremely well-designed fighter, radar was in its infancy, radio was not particularly reliable or widespread, the capability of aircraft had soared in the late 1930s, Japan's military had had years of experience fighting China, the British were fighting Nazi Germany and Italy alone (and were stretched much too thin), the US was stuck in an isolationist rut, and there was still ongoing negotiation between the US and Japan.
The British didn't think the Japanese would be crazy enough to declare war on themselves and everyone in the Pacific--including their main source of oil, the United States. The US didn't think Japan would be so brazen as to attack the US on its own soil, let alone without a declaration of war or even ending negotiations first.
And the US (and Britain and Australia) didn't lose millions of lives in the Pacific. The island hopping strategy, combined with many other things, ensured that storming well-defended island fortresses happened only when strictly necessary; the rest were bypassed, reduced by air power and naval blockade, and left to starve.
edit: nearly all sailors saw Japan as being a simple one or two week voyage, blow the japs up, be home in time for dinner.
I'm pretty sure that mentality died along with the attack on Pearl Harbor. You don't defeat an enemy an ocean away in one or two weeks after they sank all of Battleship Row. Also, Roosevelt's address did explicitly say "No matter how long it make take us to overcome this"--not something you'd say if a quick war is even remotely reasonable to expect.
