If Kim Jong-Il, the dictator of North Korea, persists in throwing ballistic missiles over the Pacific Ocean, as he did on Sunday, he may eventually induce the Japanese to shed the semi-pacifist policy they have adhered to ever since the Second World War. A buildup of armaments in Japan would worry and anger the Chinese government, which is why China should be talking less about keeping down tension levels in the region and doing more to restrain Mr. Kim.
The South Koreans live constantly with North Korean brinksmanship, and at first seemed blasé about the launch of the Taepodong-2 missile. But on Monday the Prime Minister, Han Seung-soo, said in the South Korean parliament that the government might revisit its commitment not to acquire missiles with a range longer than 300 kilometres, under the Missile Technology Control Regime.
Japan, however, is the only country that has ever suffered an attack by nuclear weapons. After decades of militarism and imperialism up to 1945, it took the opposite course, with the result that the Japanese contribution to preserving order in the world is remarkably small in proportion to the country's wealth.
After Mr. Kim's latest provocation, 78 per cent of Japanese respondents to a poll by the Yomiuri Shimbun newspaper wanted stronger sanctions against North Korea and 88 per cent said they were anxious.
Popular support in Japan for a much stronger military capacity is weak, as yet. But the North Korean missile has re-energized discussion of a Japanese pre-emptive strike capacity, and the Japanese military did deploy its missile defences on both sea and land.
In the last few years, Chinese-Japanese relations have improved, but they will decline again if China sees one of its neighbours gaining military strength. It is not in Beijing's interests to allow an arms race to develop around the Sea of Japan.
The rulers of China have every reason to use their very substantial leverage over Mr. Kim - almost all of North Korea's northern border is with China - to rein in his aggressive actions.
Follow us on Twitter: