FOR most countries, the spectacular failure of a rocket launch would mean a return to the drawing board, or at least some introspection aimed at figuring out what went wrong. But that does not appear to be the case in North Korea, where the flubbed launch of its long-range Unha-3 rocket has merely set the stage for a new level of defiance: the detonation of yet another nuclear device, perhaps bigger than in the past.The world, it seems, must be shown that North Korean scientists, despite their dearth of success in producing food, have mastered how to produce a weapon of mass destruction. And such a demonstration might well be needed to confer legitimacy on the newly installed third-generation leader, Kim Jong-un, a boy-dictator whose only accomplishment to date has been to prove on television that he can ride a horse, and that he appears to know how to read.There used to be a measure of sympathy in Asia for the plucky North Koreans and their systematic defiance of the United States and the rest of the international community. But those days are over. As the unanimous adoption of a United Nations Security Council statement on April 16 suggests, no one, including the Chinese, is trying the make the case any more for nuance in dealing with the North.The Chinese, in particular, appear to have lost patience. Reportedly, in the run-up to the rocket launch, the North Koreans refused to respond to China’s pleas that they stand down. The Chinese have had centuries of experience dealing with problems on the Korean Peninsula, the most difficult of imperial China’s tributary small neighbors, but not even receiving a reply to their communications was a new insult.If the North Korean problem is ever to be solved, it will be when China says that it has had enough. That day may be approaching, but, in the meantime, there are worrisome signs that China’s trade and investments in North Korea, the latest of which is a Chinese supermarket in which local currency can be traded at free-market (that is, black-market) rates, could oddly make China dependent on the North.Chinese traders and investors have in recent years moved in as Japan and South Korea, two of North Korea’s longstanding trade partners, have withdrawn, owing to official sanctions and increasing public irritation with the North’s intransigent behavior. China’s trade with North Korea has increased from around $1 billion in 2005 to more than $5.1 billion in 2011. The overall pattern is familiar: China imports North Korean raw materials, such as coal, and exports machinery, consumer goods, and refined petroleum products.China’s government has justified this burgeoning trade by claiming that North Korea will come to appreciate the wonders of a market economy. But that is simply an attempt to make a virtue out of necessity: for a country with one of the world’s largest and most storied bureaucracies, China has a surprisingly difficult time telling its business community not to do business with someone, especially a historic friend and ally.Chinese leaders’ longstanding reluctance to participate in international sanctions is often attributed to their belief in judging actions by whether or not they work. Perhaps the real pragmatism on display in the case of North Korea is a reluctance to rein in the business community at a time of slower growth and internal fixation.China’s rise is one of the most studied developments of our time. It is, after all, a country that can be described as a civilization, and its trajectory has been far more impressive than that of any North Korean rocket. It has emerged from what it calls a "century of shame” to become one of the world’s engines of economic development and cultural and intellectual achievement. To visit China is to be stunned by its accomplishments across the range of human endeavor.But, as many Chinese acknowledge, their country still has much to do, both internally and in its dealings with the rest of the world. Some of that unfinished business consists in reconciling past commitments with current interests. All countries carry some burden from the past, and China is no exception. But the burden of protecting North Korea from the world’s justified outrage is one that China cannot afford to carry for long.Now would be a very good time for China, as the expression goes, to put its money where its mouth is. China should follow up on its Security Council vote to condemn North Korea’s behavior by shutting down bilateral trade.Christopher Hill, currently Dean of the Korbel School of International Studies at the University of Denver, was one of the main architects of American diplomacy in the 1990’s and 2000’s.Copyright Project-Syndicate.org