FROM THE MOMENT last fall when Shinzo Abe reclaimed the office of Japanese prime minister that he had bungled away five years earlier, one question has stood out: Would he restrain his nationalist impulses — and especially his historical revisionism — to make progress for Japan?

Until this week, the answer to that question was looking positive. Mr. Abe has taken brave steps toward reforming Japan’s moribund economy. He defied powerful interest groups within his party, such as rice farmers, to join free-trade talks with the United States and other Pacific nations that have the potential to spur growth in Japan. He spoke in measured terms of his justifiable desire to increase defense spending.

This week he seemed willing to put all the progress at risk. Asked in parliament whether he would reconsider an official apology that Japan issued in 1995 for its colonization of Korea in the past century, Mr. Abe replied: “The definition of what constitutes aggression has yet to be established in academia or in the international community. Things that happened between nations will look differently depending on which side you view them from.”

Officials in South Korea and China responded with fury, and understandably so. Yes, history is always being reinterpreted. But there are such things as facts. Japan occupied Korea. It occupied Manchuria and then the rest of China. It invaded Malaya. It committed aggression. Why, decades after Germany solidified its place in Europe by facing history honestly, are facts so difficult for some in Japan to acknowledge?

We understand that South Korea and, to an even greater extent, China at times stoke anti-Japan sentiment for domestic political purposes. China distorts its own history and, unlike Japan, in many cases does not allow conflicting interpretations to be debated or studied. But none of that excuses the kind of self-destructive revisionism into which Mr. Abe lapsed this week.

An inability to face history will prejudice the more reasonable goals to which South Korea and China also object. Mr. Abe has valid reasons, given the defense spending and assertive behavior of China and North Korea, to favor modernization of Japan’s defense forces. He has good reason to question whether Japan’s “self-defense” constitution, imposed by U.S. occupiers after World War II, allows the nation to come to the aid of its allies in sufficient strength. But his ability to promote reform at home, where many voters remain skeptical, and to reassure suspicious neighbors plummets when he appears to entertain nostalgia for prewar empire.