WASHINGTON — Last month Japanese officials once again visited the controversial Yasukuni Shrine, which many Asians deplore as a symbol of Japan’s militaristic past. Soon afterward, South Korea celebrated a law passed in 1900 that claimed sovereignty over the Liancourt Rocks, a disputed outcropping in the waters between the countries.

Animosity between Japan and Korea is nothing new. But these latest events have taken relations to a new low and threaten American interests just as President Obama has embarked on a new effort to improve Washington’s position in the region.

Korean-Japanese tensions date from Japan’s invasion of the Korean Peninsula in the late 16th century. But the sorest point remains Japan’s 35-year occupation of Korea through the end of World War II. Japan may have lost the war, but the Japanese have maintained an attitude of national superiority over Koreans, which is matched by a Korean sense of resentment and outrage....