No one knows how long it would take Japan to go nuclear, though estimates are days or weeks. But for 60 years Japan has refrained from becoming a nuclear power and remained militarily quiescent. That particular sun may be rising again, however, thanks to the support by China and South Korea for the military threats of North Korean dictator Kim Jong Il.

This is the meaning of a remarkable, but underreported, comment this week that Japan might want to knock out North Korea's missile bases with a pre-emptive military strike. "If we accept that there is no other option to prevent an attack . . . there is the view that attacking the launch base of the guided missiles is within the constitutional right of self-defense," said Chief Cabinet Secretary Shinzo Abe. "We need to deepen discussion." The head of Japan's Defense Agency made a similar observation.

Article 9 of Japan's 1946 Constitution bars military force in settling international disputes and prohibits Japan from maintaining a military for the purpose of warfare. Even so, Japan has 243,000 men under arms and one of the world's most technologically capable militaries. Only the U.S., Russia and China spend more on defense.

The discussion Mr. Abe refers to has already begun -- and in part he is only reflecting public opinion. North Korea's first Taepodong missile test, in 1998, shocked many Japanese and elevated national security as a political issue, leading to the election of hawkish Prime Minister Junichiro Koizumi in 2001. Virtually every poll since last week's North Korean test also shows overwhelming public anxiety about North Korea and support for a strong response.

Mr. Koizumi, who leaves office in September, has talked repeatedly about Japan becoming a "normal" nation, by which he means accepting more responsibility for its own defense and playing a greater role in international security. Japan has already greatly expanded joint military ties with the U.S., including a deployment of 600 noncombat troops to Iraq -- its first since World War II to a country where fighting is still in progress.

Next up for reform may be the pacifist constitution, to which Mr. Koizumi has proposed major revisions, including jettisoning Article 9. Mr. Abe -- the leading contender to succeed Mr. Koizumi as PM -- also favors constitutional revision. As a first step, the Koizumi government introduced a bill in the Diet last month to upgrade the Defense Agency to full-fledged Cabinet status.

Japan's new assertiveness is also on view at the United Nations, where it has taken a tough stance after Pyongyang's missile tests and is leading the effort to forge an international response. A Yomiuri Shimbum poll finds 90% of respondents favor Japan's proposed resolution, which would ban the transfer of anything North Korea could use in its nuclear or missile programs.

Meanwhile, back in East Asia, the reaction of China and South Korea to the Pyongyang missile tests can only encourage Japan in thinking it needs a stronger military. China has threatened to veto Japan's U.N. resolution. And in Seoul this week, a presidential spokesman mustered more anger at Mr. Abe's remarks than any South Korean official has against the North's military provocation. The spokesman accused Japan of using the missile tests as "a pretext for becoming a military power." But the truth is that by propping up the Kim regime and letting his nuclear and missile threats continue, South Korea is itself helping to revive Japan's military power.

Northeast Asia has prospered as much as any place in the world since the end of the Korean War, thanks to the peace and security provided by the U.S. military. We'd prefer to see that status quo continue, but North Korea's provocations have introduced a threatening new instability. Tokyo has wisely understood the benefits of staying under the American nuclear umbrella, but once domestic political and nationalist impulses start to stir, they can be hard to contain.

China and South Korea may think they can prop up Kim at little cost, save for America's discomfort. But the combination of China's strategic cynicism toward a client dictatorship and South Korea's naive appeasement is making that neighborhood a much more dangerous place. If North Korea continues to defy the world and the world continues to do nothing, a more militarily assertive, and probably nuclear-armed, Japan is inevitable.

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