This isn’t the first time the flyspeck islets have provoked a crisis. Back in April 2006, South Korea’s then-president Roh Moo-hyun threatened force, sending gunboats to prevent Japanese coast-guard vessels from mapping the nearby seabed. According to a U.S. State Department cable disclosed by WikiLeaks, Washington feared that Seoul might “do something crazy.” Thomas Schieffer, then America’s ambassador to Tokyo, told Japan’s vice foreign minister at the time that “the Koreans are behaving irrationally” and warned him that “everyone needs to back off.” The Koreans and Japanese finally did as he urged, and the situation cooled down.

This time, however, things have turned so messy that neither side may be able to back down from its nationalist posturings. In early August, South Korea’s President Lee Myung-bak crossed a red line for the Japanese when he became the first leader of his nation ever to visit the disputed islands. Japan’s resentment only worsened the next day, when South Korea’s national soccer team defeated the Japanese in the bronze-medal match at the London Games—and then, after the final whistle, a South Korean midfielder stood on the pitch and hoisted a sign declaring “Dokdo is our territory.” (Although the player was barred from the medal ceremony and his award was withheld pending an investigation of the incident by the International Olympic Committee and FIFA, soccer’s international governing body, he has since been exempted from compulsory military service and named to his country’s World Cup team.)

Four days after Lee’s surprise trip to the rocks, the president delivered an even more stinging slap to Japan. Out of the blue, he announced that if Emperor Akihito ever expects to visit South Korea, he should first apologize for Japan’s colonial rule of the peninsula before and during World War II. Many Japanese regarded Lee’s words as an insult to the emperor, and Japan’s legislators once again asserted their country’s claim to the islets. Last week Prime Minister Yoshihiko Noda infuriated the South Koreans on another sore topic, saying there’s no evidence that proves Japan’s imperial army forced Korean women to work as sex slaves. This week South Korea intends to hold military exercises on the disputed islets, and Japan is pondering whether to scrap a currency-swap deal with Seoul.

The falling-out is cause for concern not only in Seoul and Tokyo but in Washington as well. Both are vital U.S. trading partners and America’s most important allies in Asia, but more than that: cooperation between them is essential in keeping North Korea in check. And yet their quarrel has grown downright juvenile. When Noda sent Lee a letter of complaint, the South Korean president declined to accept it, instead returning it via a Korean diplomat stationed in Tokyo. The Koreans later mailed Noda’s letter to the Japanese Foreign Ministry. “I’m sorry, but they’re behaving like kids in a scuffle,” said a disgusted Tsuyoshi Yamaguchi, Japan’s senior vice foreign minister. In the end, Tokyo accepted the letter’s return, rather than “tarnish the dignity of Japanese diplomacy,” as Noda put it—advising South Korean officials at the same time to cool their jets.

Japanese officials struggled to make sense of Lee’s actions. The Korean president had always been viewed as a pragmatist, more interested in building a “future-minded relationship” with South Korea’s third-largest trading partner than in dwelling on past misdeeds. “What happened to the guy?” Noda blurted out during a parliamentary session. The most popular explanation points to Lee’s approval ratings, which had sunk to a pitiful 17 percent. There’s a vicious cycle that has prevailed ever since the advent of democratic rule in the late 1980s. Every five years, a new president sweeps into office, pledging better relations with Japan. But by his third or fourth year in office, the administration gets ensnared in a corruption scandal, and the president becomes a lame duck. (In July, Lee found it necessary to apologize publicly for a scandal involving his brother.) To rescue what’s left of his presidency, he resorts to anti-Japan rhetoric, and relations with Tokyo deteriorate—a trend that has grown stronger, especially in the past decade.