There is a difference between defeating a country in a war using conventional weapons, and dropping two Atom Bombs on a country the size of New Jersey.
That difference would be about 1 million civilians killed. I would have a little bit of a chip on my shoulder if that happened to the US.
Its also is a large part of their culture. Eastern nations have always looked down on Western nations as barbaric in a way. When China was first discovered by the West, Western nations feared them because the Chinese talked the talk, but when push came to shove they couldn't walk the walk.
The Japanese on the other hand had their collective asses handed to them in WW2, but then they decided to hand us out collective asses in the trade department. So I think that feeds their nationalism more.
__________________
|