It appears that North Korea's kooky leader, Kim Jong Il, did exactly what he said he'd do: conduct Pyongyang's first nuclear-weapons test.

Sadly, we've got more than Pyongyang's (worthless) word on this: Seismic data seems to confirm the explosion, though some suggest it was a ruse - a large conventional explosion, not an actual underground nuclear blast.

If it was a nuke, what's the likely global fallout? The consequences are deadly serious for American interests - and a watershed event for international security as Pyongyang becomes the ninth member of the once-exclusive nuclear-weapons club.

Take Northeast Asia. Relations among the regional major powers - Japan, China and South Korea - were already tense. North Korea's atomic firecracker certainly won't help.

Japan and South Korea may feel obligated to go nuclear themselves. Japan, with a large nuclear power industry and a top-notch scientific community, could go nuclear in a flash.

South Korea similarly. While the South Korean government is generally conciliatory toward the North, if Seoul's historical rival Tokyo goes nuclear, it might feel compelled to do so as well out of pride as much as for security.

The U.S. pledge to consider an atomic attack on either Japan or South Korea by North Korea as an attack on America was clearly intended to deter Kim as well as to encourage the others to hold off on splitting atoms. But even if Japan and South Korea decide against the nuclear option, they might instead engage in a conventional arms buildup to deter North Korea.

Such a significant arms buildup would affect the security policy of other Northeast Asia powers. China, Taiwan and/or Russia might respond in kind - resulting in a dangerous conventional (or nuclear) arms race.

And we have a lot at stake in the region's stability with 70,000 troops based in Japan/South Korea, and another 10,000 sailors at sea in the western Pacific at any one time. (And major economic interests, too.)

A North Korean bomb also encourages other rogue states - and stateless groups - to try to follow suit; indeed, Kim might help out. Iran is the biggest concern. Pyongyang has worked closely with Tehran on ballistic missiles and nuclear issues in the past. The sharing of scientific data from North Korea's underground blast might shorten the timeline for Iran to achieve nuclear statehood. (Heck, Syria could conceivably become a North Korean nuclear client, too.)

Of course, the worst scenario of all is for al Qaeda or another nuke-seeking terrorist group to come knocking on indigent North Korea's door with a wheelbarrow of cash. While transferring a fully functional nuclear weapon to terrorists is extremely risky business for any state, the possibility isn't limited to the realm of pulp-fiction thrillers.

North Korean nukes also expose us to a growing threat. Pyongyang must still "weaponize" its test rig into a bomb/warhead - as well as perfect missiles capable of reaching the United States. But it may be able to do this in the coming years.

At this point, diplomacy or even economic sanctions are unlikely to walk North Korea back: When it comes to nukes, few nations have ever disarmed. The only practical answer is containment, military deterrence - buttressed by missile defense - and strong regional alliances.

Peter Brookes, a senior fellow at The Heritage Foundation, is the author of "A Devil's Triangle: Terrorism, WMD and Rogue States."