Military brilliance. By the time of the attack on Pearl Harbor Japanese-American foreign relations had deteriorated to the point that war was inevitable. Japan's militarism and designs on Asia had forced the US into an old fashioned conflict over Pacific Rim dominance(similar to what is emerging with China). The result was a struggle between the United States, supporter of free trade and Japan, seeker of natural resources - even at gun point. The conflict itself was inevitable, the attack on Pearl Harbor was bold, unpredictable and unexpected.
American Naval Academy graduates had been staging attacks on Pearl since the construction of the Pacific Fleet HQ there decades before but few people actually thought the resources and skills necessary to stage the attack existed in the Japanese Navy. It was a clear demonstration of the power of planning, secrecy and the deadliest force, still, in the world - the carrier battle group.