Since South Korea and China opened diplomatic relations in the early 1990s, the two have enjoyed extraordinarily amicable ties. Bilateral trade and commercial exchanges have exploded. Personal, cultural and educational exchanges have grown so fast that the two nations have suddenly become friends, despite the fact that China fought against South Korea to help the North during the Korean war half a century ago.
But all good things must come to an end. The two have been at odds in recent months over a part of history. Beijing has attempted to incorporate Koguryo, Korea's ancient kingdom that existed more than 2,000 years ago in the northern part of the Korean Peninsula, into Chinese history. So far, attempts have mostly been limited to academic circles. Claiming that Koguryo was a provincial regime of ancient China, scholars are in the process of restoring relics and registering them with Unesco, the UN's heritage body.
Koreans, who believe that Koguryo has been part of their history for thousands of years, are infuriated. If the Chinese interpretation were true, Korea's entire history would be reduced from 5,000 to 2,000 years, and its original territory would be halved, covering only the southern half of the Korean Peninsula, below the Han River.
Seoul has, of course, protested strongly. Officials pointed out that the Chinese Foreign Ministry website has no reference to Koguryo's history. To add to South Koreans' anger, Beijing then removed the entire ancient history of Korea from the site.
Seoul now believes that Beijing is behind what it calls an outright distortion, and is considering recalling its ambassador to Beijing.
There could be many reasons for Beijing's move, which risks a diplomatic row with Seoul. Some in Seoul argue that the Chinese government is preparing for a possible territorial or historical dispute in case the two Koreas are unified.