The United Nations Security Council resolution passed today tightening sanctions on the Democratic People's Republic of Korea is a significant U.S. diplomatic victory. Whether it will significantly retard North Korea supremo Kim Jong Un's quest for things that go boom is another question.

Let's start with at least two cheers for Susan Rice, the U.S. ambassador to the UN, who succeeded in getting China to agree, in relatively speedy fashion, to changes in the sanctions regime that are more than cosmetic.

The resolution expands the list of proscribed items, institutions and individuals, creates new financial sanctions that block illicit cash transfers and curtail North Korea's ability to finance its weapons programs, and commits the Security Council "to take further significant measures in the event of a further DPRK launch or nuclear test."

Drawing on a report issued last summer by a UN panel of experts, the resolution also tightens loopholes in the existing sanctions regime. It gives states more authority to inspect suspicious cargo and to deny port access or fly-over rights to ships or planes that refuse inspection. It encourages them to share information in a timely fashion. And it clarifies that proscribed luxury items include, but are not limited to, yachts, gems, luxury and racing cars. That may help Italian authorities the next time they face a DPRK-bound air shipment of high-end U.S.-made tap dancing shoes, which they apparently blocked.

China's willingness to go along with new measures speaks to its frustration with Kim Jong Un, whose missile-cum-satellite launches and nuclear test have provoked much Chinese hand-wringing. The North's wild threats of nuclear attack in retaliation for UN sanctions, meanwhile, point to its disappointment with its long-time patron's response. Rice's success in forging a united diplomatic front definitely puts Kim in a more awkward spot.

Yet a win at the Security Council is hardly even half the battle. For all the U.S. trumpeting about "strong" sanctions, they are really only as strong as their weakest link. And in that respect, last summer's UN report on sanctions implementation is sobering. It noted that fewer than half the UN's member states had submitted national implementation reports, with significant gaps in Africa (a regular buyer of North Korean arms), Latin America and the Caribbean. From May 2011 to mid-2012, only three countries provided inspection reports to the committee, and one of them was the U.S.

I know from my own days as a boy diplomat how ad hoc such efforts can be. Posted in Bombay during the Good Gulf War, I was theoretically responsible on my first tour (when I wasn't snuffing out the visa dreams of would-be motel operators and software engineers) for monitoring shipping. It was not my finest hour.

For all their newfound solidarity, what the Chinese say about North Korea, and what they will or can do, are three separate things. Statements by Chinese commentators in the Western press about China's willingness to cut Kim Jong Un loose should be taken with a giant chunk of MSG. Some of them are much less definitive in the Chinese-language press. Even if China were committed to cracking down on the North's illicit trade, much of which is shipped thru its ports and land borders, the scope of activity would defy all but the most determined effort. Like drug smugglers, North Korea is relying more on sealed shipping containers, and as the UN experts panel observes, only 2 percent of the world's 500 million annual ship container movements ever get inspected.

So as Zhou Enlai reportedly said in another, often miscontrued context, it's "too early to say" if this newest round of sanctions will mark an effective turning point in the world's collective struggle to constrain a truculent state. In the meantime, look for Kim to make the worst of a bad situation, perhaps with some kind of military provocation, another missile launch or a nuclear test. Then it's back to the UN, again.

(James Gibney is a member of the Bloomberg View editorial board. Follow him on Twitter.)