This is a good summary of the (international) political situation in Japan regarding nationalism and imperialism.

BBC News : Japan's agonised wrestling with its past

Identity crisis

Nearly 60 years after it surrendered to the United States and renounced the militarism of the 1930s and 40s, Japan still cannot decide what kind of country it wants to be.

This manifests itself in all sorts of ways, from the agonised debate over sending a few hundred troops to Iraq and the furious attacks on the prime minister's visits to the national war shrine, to the row today over playing the national anthem in school.

Many of the symbols of the disastrous era of military rule still survive in Japan - the emperor, the flag, the national anthem - but their exact status has been left deliberately vague.

It was only in 1999 that the ancient poem Kimigayo, calling for the reign of the emperor to last "for all eternity" was formally declared the official national anthem once again, as it had been before the war. But many Japanese still object to it.

So when the Tokyo city government this year decided to enforce playing Kimigayo at the beginning and end of the school year, hundreds of teachers registered their objection by refusing to stand up.
Toru Kondo has had an unblemished career as an English teacher for 31 years.

Now, spluttering with rage, he opens an envelope to show me his first ever official warning from the Board of Education. He is one of those who refused to stand.

"Japan changed after the war," he says. "Our constitution gives us freedom to follow our consciences. This cannot be a democratic country if they insist on punishing us."

Like many teachers in Japan, Toru Kondo's politics are left-wing, and like most left-wingers here, he has an unforgiving view of anything connected to his country's shameful past.

Never mind that the lyrics of Kimigayo are innocuous, and today's emperor has only symbolic, not divine status.
Takayuchi Tsuchiya is a city councillor who wholeheartedly backs Governor Ishihara's new rule. "Singing Kimigayo will help promote a sense of national unity," he told me.
...
Mr Takayuchi has no sympathy for rebel teachers. He dismisses them as communists who want to indoctrinate the children.
And what about the majority of Japanese who fall in between these militant guardians of Japan's history? It is almost impossible to know what they think.
...
Open debate on divisive issues is strongly discouraged for fear it would disturb social harmony.

So there has been little public soul-searching about what went wrong with Japan before World War II.