WASHINGTON -- Relations between Japan and China, the two great powers of Northeast Asia, have in recent months sunk to their worst levels at least since Tiananmen Square in 1989. This past weekend's anti-Japanese riots in China were unprecedented in the modern era, but they were only the latest in a series of highly unfortunate events.

The new Sino-Japanese tension is probably welcomed in some parts of the Pentagon. It draws Japan closer to the United States militarily -- on issues like possible conflict against China in the Taiwan Strait -- when most of the rest of Asia is being successfully wooed by China as it softens its image and increases its economic power. But left unchecked, worsening tensions between Asia's greatest high-tech power and its fastest growing economy could make for a strategic rivalry that harkens back to the Europe of the early 20th century. That cannot be good for anyone's interests.

Tension in the Japan-China relationship has powerful historical roots. Chinese citizens have never forgiven Japan for the aggression and atrocities committed during the 1930s and 1940s such as the Nanjing massacre, which left at least hundreds of thousands of Chinese dead. Ironically, during the Cold War, China did not have the luxury of nurturing such grudges -- and Japan was sufficiently penitent, or at least sufficiently muzzled by postwar guilt, not to stoke the embers of painful memories. But now a strong and increasingly nationalistic China has the capacity to dream about a stronger role in future global affairs -- and also to remember the past. Among other things it spreads a very critical message about Japan in the textbooks that its schoolchildren still read today.