As the actual experience of battle receded into the mists of history, the ethos of the samurai became more rigid and militaristic. The whole samuri ethic served just as well to shape a compliant bureaucracy as it had originally done to form a vigorous military. There was, in fact, hardly any occasion for samurai to put their martial training into practice.
The Asia-Pacific War of 1937-1945 has deep roots. It also involves a Japanese society that's been called one of the most distinctive on Earth. If there were a Japanese version of Captain America, this would be his origin story.