The first is the relatively small yield – yes, it’s larger than the first two tests, but that really doesn’t mean anything. A 10 kiloton (or 6-7 kt or 15 kt) nuclear weapon is nothing to sneer at, but as the world saw with Hiroshima and Nagasaki, a weapon of that kind isn’t much more effective than conventional explosives. The firebombings of Tokyo did more damage and took more lives than either nuclear blast in World War II.
They’ve also talked about switching their nuclear fuel from plutonium to highly-enriched uranium, which is weird and kind of a step back. The United States used to use HEU but once we perfected plutonium processing techniques we stuck with that. It’s a much more effective fuel for a multi-stage thermonuclear explosion, and it’s a little weird for anyone to change from plutonium. If true, it could indicate a processing and/or supply issue, but that would be a good sign; it would means that they’re having trouble sourcing fissile material. So they may not even have the raw materials necessary to build many bombs.
The other part is a little up in the air and I’ve heard competing claims, but nothing I’ve read so far confirms (despite Pyongyang’s claims) that North Korea has successfully miniaturized a nuclear weapon – which would be a prerequisite for mounting it onto an ICBM. It’s one of the most difficult steps in the technological scale of nuclear science and requires increasing reaction efficiency. The small gain in yield this test provided makes me think that they definitely haven’t reached that step yet. I’m also not positive on the physics – and it might just be a coincidental concurrence rather than cause – but I believe the only miniaturized, i.e., ICBM warheads in existence are thermonuclear, and a failure to demonstrate that technology definitely means something.
So, in short, I’m not worried yet. They can’t build very many bombs; the bombs they can build aren’t especially powerful; they have no missile with the range to reach the United States and even if they did they haven’t miniaturized a warhead sufficiently to mount on it; and their only means of delivering one of the few extant bombs is by bomber, which exist in low numbers and also don’t have the range to hit the US, much less reach here undetected. So we’re all safe over here for the foreseeable future.
I don’t know that this really changes anything strategically even in the region. We’ve known, the South Koreans have known, and the Japanese have known; it’s common knowledge that North Korea has some nuclear weapons. And that hasn’t led to regional proliferation or a move to oust the Kim regime or anything like that. I don’t see “just another test” making a dramatic difference on that front. Dr. Farley probably says it best: “Last night, North Korea expended a significant fraction of its fissile material to achieve nearly nothing, beyond possibly the irritation of Beijing and the strengthening of right-wingers in Japan and the United States.”
Yeah, great job there, Pyongyang.