Washington

NORTH KOREA as we know it is over. Whether it comes apart in the next few weeks or over several months, the regime will not be able to hold together after the untimely death of its leader, Kim Jong-il. How America responds — and, perhaps even more important, how America responds to how China responds — will determine whether the region moves toward greater stability or falls into conflict.

Mr. Kim’s death could not have come at a worse time for North Korea. Economically broken, starving and politically isolated, this dark kingdom was in the midst of preparations to hand power over to his not-yet-30-year-old son, the untested Kim Jong-un. The “great successor,” as he has been dubbed by the state media, is surrounded by elders who are no less sick than his father and a military that chafed at his promotion to four-star general last year without having served a day in the army. Such a system simply cannot hold.

The transition comes at a time when the United States has been trying to get nuclear negotiations back on track. Those efforts have now been replaced by a scramble for plans to control loose nuclear weapons, should the regime collapse.

And yet Washington remains powerless. Any outreach to the young Mr. Kim or to other possible competitors could create more problems during the transition, and would certainly be viewed as threatening by China. Since Kim Jong-il’s stroke in 2008, the United States and South Korea have been working on contingency plans to deal with just such a situation, but they all thought they would have years, if not a decade.