When Japan’s government recently decided to ignore Chinese protests and allow Taiwan’s former president, Lee Teng-hui, to visit Japan, China lashed out at its Asian neighbor, even threatening retaliation. But this latest dispute is characteristic of a remarkable flurry of anti-Japanese activity in China since 2003.

That August, construction workers in Qiqihar mistakenly ruptured mustard gas canisters left from the wartime Japanese occupation, injuring dozens and killing at least one. The reaction by China’s public to the gory photos of the injured was furious. One million signatures were rapidly gathered on an Internet petition demanding that the Japanese government thoroughly resolve the chemical weapons issue, while Internet chat rooms filled with anti-Japanese invective.

Two weeks later, 400 Japanese businessmen hired as many as 500 local Chinese prostitutes for a weekend sex party in a Zhu Hai hotel. Racy reports in China’s press sparked another round of righteous fury, drawing on the trope of China as a raped woman, an image long suppressed under Mao. Occurring on the 72nd anniversary of the 1931 Mukden Incident that led to the Japanese occupation of Manchuria, 90% of Chinese respondents to an Internet poll said they believed that the Japanese businessmen intended to humiliate China.

The following month, at a party thrown by Northwestern University in Xian, three Japanese students and one of their Japanese teachers performed a skit, during which they pranced around the stage with red bras over their t-shirts. In Japan, such skits are apparently regarded as humorous; in China, the skit was seen as lewd and insulting. The Japanese students received death threats. Thousands of Chinese demonstrated on campus and through the city, shouting “Boycott Japanese goods!” and “Japanese dogs, get out!” A Japanese flag was burned outside the foreign students’ dorm. Even though the Japanese students apologized, they were expelled.

Then, last August, during the Asian Cup soccer tournament, Chinese fans in Chongqing, Jinan, and Beijing hurled insults at the Japanese team – and bottles at their team bus. During the Cup final between China and Japan in Beijing, which Japan won, Chinese fans reportedly chanted “Kill! Kill! Kill!” and “May a big sword decapitate the Japanese!”

Sino-Japanese amity was hardly enhanced in mid-November, when a Chinese nuclear sub encroached into Japanese waters. Nor did it help when Chinese Premier Wen Jiabao snubbed Japanese Prime Minister Junichiro Koizumi’s invitation to visit his country.

Why has this popular nationalism emerged? And why is it directed at Japan? The short answer is that after a quarter-century of economic reform, Chinese today are much freer to express themselves. Under Mao, when the Chinese Communist Party sought accommodation, diplomatic recognition, and overseas development aid from Japan, Chinese were not allowed to confront their past victimization at the hands of Western and Japanese imperialism. Today, however, Chinese are facing past atrocities from the “Century of Humiliation” that ended with the Communist takeover in 1948, and a long suppressed anger has resurfaced.

To most Chinese, the Japanese are paradigmatic “devils,” not only because of the brutality of Japanese imperialism and the sheer number of Chinese killed by Japanese troops. Anti-Japanese anger has an ethical justification rooted in the perceived injustice of “little brother” Japan’s impertinent behavior towards “big brother” China, from China’s loss in the Sino-Japanese Jiawu War and the humiliating Treaty of Shimonoseki of 1895 to the insulting “21 Demands” of 1915 and on to WWII atrocities like the Rape of Nanking. The complexity and depth of these anti-Japanese sentiments helps sustain them and sets them apart from other, more fleeting and contradictory anti-foreign sentiments, such as those Chinese sometimes harbor towards Americans.

The emergence of a deep-rooted and popular anti-Japanese enmity in China does not bode well. As the Party uses nationalist sentiment to keep China unified, these sentiments have become fiercer, and the political leadership is increasingly held hostage to nationalist opinion in formulating China’s foreign policy towards Japan. As a result, Japanese increasingly fear China’s rise and possible future retribution for their country’s wartime aggressions. Indeed, Japanese public-opinion surveys also reveal a marked decline in favorable views of China.

Meanwhile, an emergent Japanese nationalism argues that Japan should revise its pacifist constitution and develop its military capability – possibly including nuclear weapons to balance threats like that from North Korea. The possibility of a Sino-Japanese arms race is becoming increasingly real. Indeed, the Japan Defense Agency recently outlined three scenarios for a Chinese attack against Japan, and announced that it is planning to redeploy its troops from the north (where they were originally stationed to defend Japan against the former Soviet Union) to the south, facing China.

Pessimists now fret that Asia is not big enough for both China and Japan: you “can’t have two tigers in one forest.” Optimists counter that China and Japan can cooperate, acting as the “dual engines” of Asian development. Japan expert Feng Zhaokui takes the middle ground, arguing that Sino-Japanese relations will be marked by the coexistence of both cooperation and conflict.

Recent developments suggest that a purely cooperative bilateral relationship is unlikely, to say the least. If we are lucky, Feng may be right. But if we are not, we could witness the emergence of a new and dangerous political fault line in East Asia.