An important factor is being overlooked in all the clamor surrounding the test of a North Korean nuclear weapon: despite the bold show at flouting international norms, Kim Jong—Il is, in fact, making a carefully—calculated effort to stay within the lines.

Sunday's explosion is the first time in history that a national nuclear capability has been debuted in an underground test.

All previous such events, beginning with the Trinity shot in July 1945, were above—ground, open—air exercises. This was standard practice for the first two decades of the atomic age. Hard as it may be to believe, atmospheric nuclear test explosions were a nearly   monthly occurrence during the 50s and early 60s, with the U.S. and USSR setting off hundreds of bombs along with several dozen more by the UK, France, and China.

Public outcry over the perils of radioactive fallout (particularly strontium—90, a nasty isotope that settled in the bones) in the early 60s put an end to the practice. The ban was   formalized by the Limited Test Ban treaty of 1963,    which prohibited bomb tests 'in the atmosphere, in outer space, and under water'. Unlike many such treaties, the Test Ban treaty has been scrupulously observed by all signatories since it went into effect. Among non—signatory countries, only China and predictably, France, chose to defy the treaty.

North Korea is not a signatory. So the question arises — why did Kim Jong—Il, a man with  no perceptible limits regarding either flamboyance or illegality, choose the less provocative (and impressive) route of exploding his bomb underground? (Or bombs, if reports of a second blast are true — though the 'less than one kiloton' yield makes it seem unlikely. Could this represent a fizzle yield?)

The 'no room' argument won't do. There is plenty of waste space in North Korea (I have several relatives who passed through circa 1950 who can testify to this), and in any case, Kim has never revealed much in the way of concern over the health of his subjects. No more than he has over that of the citizens of neighboring countries (this is, after all, the man who launches missiles through other people's airspace), so the fallout objection has to go too.

Which leaves us with the intuition that this is the act of a man who has stepped beyond his personal limits and is unsure of how far he can go. By refusing to violate the ban on atmospheric tests, Kim has disclosed a sense of calculation not detectable in his previous actions. This is not a man who has lost control or is about to go over the edge. This is a man who is carefully calibrating every step to discover exactly what he can get away with.

Kim has revealed, without at all intending to, that he's not ready to go to the mattresses quite yet.

This new note of hesitation goes a long way toward taking the wind out of his sails. Kim has gotten as far as he has by acting like the neighborhood psycho. Many readers will recall the brain—damaged crack addict who terrorized a street in uptown Manhattan for several years in the late 80s and early 90s. The cops couldn't arrest him, the judges washed their hands of him, the locals were too frightened to confront him, so he lorded it over the entire street, smashing car windows, chasing women and children, assaulting passersby, until at last he tossed a small girl into the traffic, and it was hello, Ward D.

This is the exact role that Kim has played, with his border massacres, raids and   assassinations, and missile sprees. The entire East Asian littoral has acted like terrified brownstone dwellers, the U.S. like the cop whose hands are tied, the UN, like... well, that would be an insult to the judges.

But now it's over. With the single error of burying his nuclear test instead of the more characteristic move of setting it off above ground for the world to goggle at, Kim has trashed his carefully—wrought image. He's no longer the international lunatic who must be handled with kid gloves for fear of the consequences, but a clever bully out to get what he wants by whatever means that doesn't threaten his security.

Kim may well be holding an atmospheric test in reserve, in order to ratchet up the tension up some future point. Or who knows, he may set off six at once to match his great July 4th missile tantrum. But that will be too late. The mask has slipped, revealing a man a little less confident and a lot more cautious than anyone might have guessed. The world should respond accordingly.

J.R. Dunn is a frequent contributor, and former editor of the International Military Encyclopedia.