As tensions between China and Japan continue to escalate, both sides can take solace knowing that things could be much worse. And not long ago, they were. In 2005, large demonstrations broke out in Beijing, Shanghai and Guangzhou and other Chinese cities in response to Japanese efforts to win a permanent seat on the U.N. Security Council and a Japanese history textbook that downplayed its wartime aggression. Protesters smashed windows of Japanese restaurants and other businesses, and police struggled to control thousands of demonstrators who surrounded the country's embassy in Beijing, some hurling rocks and bottles over the compound's gates.

On Saturday Chinese demonstrators gathered at the Japanese Embassy once again. The date was the 79th anniversary of the Mukden incident, a plot by Japanese Imperial Army officers that helped provoke the Japanese invasion of Manchuria. This time the antagonism was over unoccupied islets in the East China Sea known as the Diaoyu in Chinese and the Senkaku in Japanese. Japan has administered them since the early 1970s, when the U.S. ended its post – World War II control. But China and Taiwan also lay claim to them, and the likelihood of oil and gas reserves in the surrounding seabed has raised the stakes of the dispute. On Sept. 7, Japan detained a Chinese skipper after a collision between his fishing boat and two Japanese coast guard vessels happened near the islands. While Japanese authorities released the boat's 14 Chinese crew members, captain Zhan Qixiong is still being held while he is investigated for "obstructing officers on duty." Zhan, 41, could face three years in prison....