To many Americans, Zen Buddhists primarily devote themselves to discovering inner serenity and social peace. But Zen has had strong ties to militarism -- indeed so strong, that the leaders of one of the largest denominations in Japan have remorsefully compared their former religious fanaticism during Japan's brutal expansionism in the 1930's and 40's to today's murderously militant Islamists.

The unexpected apology for wartime complicity by the leaders of Myoshin-ji, the headquarters temple of one of Japan's main Zen sects, was issued 16 days after 9/11, which gave it a particular resonance. But the leaders of Myoshin-ji -- as well as other Zen Buddhist leaders who have also delivered apologies over the past two years -- mainly credit a disillusioned Westerner for their public regrets: Brian Victoria, a former Methodist missionary, who is a Zen priest and historian.

Buddhist leaders in Japan and the United States said in recent interviews that Mr. Victoria had exerted a profound influence, especially in the West, by revealing in his 1997 book, ''Zen at War,'' a shockingly dark and unfamiliar picture of Zen during World War II to followers who had no idea about its history. Keiitsu Hosokawa, secretary general of Myoshin-ji, made a speech to the group's general assembly in September 2002 in which he said that the Japanese edition of ''Zen at War'' had been one of several factors that ''provided the impetus'' to issue the group's apology.

Now, in a new sequel called ''Zen War Stories,'' Mr. Victoria has dug more specifically into relationships between Zen leaders and the military during World War II.