HIROSHIMA -- The walk from my hotel to the conference center took me past the Atomic Dome and through the Peace Park that commemorates the atomic bombing of Aug. 6, 1945. Friday morning, several fire trucks were parked in front of the Children's Peace Monument; someone had torched two display cases that contained 140,000 origami cranes. The conference organizer said that happens every month or so.

It's tempting to see the violence in the middle of the peace park as symbolic: a reflection of Japan's ambivalence about its status as the world's only atom-bombed nation, and the pacifism it has nurtured, and the fact that the country rests comfortably under the U.S. nuclear umbrella. Perhaps no one in Japan feels that unease more acutely than the citizens of Hiroshima.

The country's sense of vulnerability has increased. The North Korean nuclear crisis has underscored its exposure to the threat of missiles and the weapons of mass destruction that they can carry. During my stay, newspapers headlined last week's Pentagon report on China's military and the modernization of missiles that could target U.S. forces in Okinawa.