It was about 15 years ago, recalled Yoshiaki Yoshimi, a mild-mannered historian, that he grew fed up with the Japanese government's denials that the military had set up and run brothels throughout Asia during World War II.

Instead of firing off a letter to a newspaper, though, Yoshimi went to the Defense Agency's library and combed through official documents from the 1930s. In just two days, he found a rare trove that uncovered the military's direct role in managing the brothels, including documents that carried the personal seals of high-ranking Imperial Army officers.

Faced with this smoking gun, a red-faced Japanese government immediately dropped its longstanding claim that only private businessmen had operated the brothels. A year later, in 1993, it acknowledged in a statement that the Japanese state itself had been responsible. In time, all government-approved junior high school textbooks carried passages on the history of Japan's military sex slaves, known euphemistically as comfort women.

"Back then, I was optimistic that this would effectively settle the issue," Yoshimi said. "But there was a fierce backlash."

The backlash came from young nationalist politicians led by Shinzo Abe, then a little-known lawmaker in the long-governing Liberal Democratic Party, who lobbied to rescind the 1993 admission of state responsibility. That long-cherished goal seemed close at hand after Abe became prime minister in September.