North Korean leader Kim Jong Il decided long ago that nuclear weapons were his best protection against an external threat of regime change. In ill health and preparing his youngest son, 'Brilliant Comrade' Kim Jong Un, to succeed him, Kim seems to have decided that the bomb also is crucial to staving off an internal threat to the family dynasty that has ruled the hermit state since its founding. His powerful military wants a nuclear deterrent, and Kim wants to deliver it by 2012. That explains the urgency in his nuclear and missile tests, and makes the prospect of nuclear disarmament doubly difficult. The pending succession adds a layer of uncertainty and risk to North Korea's standoff with the West. That standoff is playing out on the high seas and in high finance. The Navy is trailing a rusty North Korean cargo ship believed to have been ferrying missile parts for sale to Myanmar. U.N. sanctions to cut off North Korea's arms trade, which were enacted after Pyongyang's second nuclear test on May 25, allow the United States and its allies to intercept the ship. The North Korean government declared that would be an act of war and threatened to 'wipe out the aggressors on the globe once and for all' if it considered itself to be under attack. But the ship apparently is turning back now, after U.S. moves to freeze assets and isolate companies that facilitate North Korea's weapons trade. Pyongyang, meanwhile, is poised to test-fire more missiles, possibly in time for the July 4 holiday, and the U.S. has put defense systems on alert. President Obama says he'd like to break the cycle in which North Korea provokes an international crisis to extract aid and concessions from global powers that are trying to sanction Pyongyang into abandoning its nuclear ambitions. The key to ending this brinkmanship, however, lies not with Kim but with Beijing. China is North Korea's main Communist ally and trading partner, and although it would like to see an end to Pyongyang's nuclear program, it has so far demonstrated greater concern about the prospect of regime collapse that would likely create an economic crisis in the region. China's patience seems to be wearing thin, as it did sign on to the June 12 U.N. resolution. Obama's coordinator on the resolution, Ambassador Philip Goldberg, is in China this week and must work to convince the government that further steps are needed. A credible threat from Beijing to cut off trade could persuade Pyongyang to give up on nuclear weapons. As with Iran, Obama should make clear to Kim that Washington seeks nuclear disarmament, not regime change. At the same time, he should make clear to China that if the North Korean regime were to collapse, the United States and its allies would help share the economic burden. 