Perhaps Kim Jong Il's most enduring legacy was to turn North Korea into a nuclear weapons state. The country successfully tested a nuclear bomb underground in 2006, and a second test followed in 2009.
With Kim's death, which was announced Monday, his presumed successor is his son, Kim Jong Un. But little is known about him or his thinking on the country's nuclear program.
Reliable details about North Korea's nuclear weapons are also hard to come by, but North Korea is believed to hold between four and 10 nuclear bombs. All are made from plutonium, which the North has manufactured since the early 1990s. There is currently no plutonium left in the stockpile — it's all been turned into bombs.
North Korea does have more than 100 tons of fresh nuclear fuel rods that could be inserted into an active nuclear reactor, which could produce more plutonium.
But Joel Wit, an expert on North Korea at the Johns Hopkins School of Advanced International Studies, says North Korea hasn't done that.
"Essentially over the past few years, they haven't produced any," he says.
The reason why they haven't produced more plutonium is something of a puzzle.
"They haven't restarted this reactor that was shut down under President Bush, although they've threatened to do it many times," Wit says. "So if they did restart it, they could load it up with these fuel rods."
North Korea has agreed to shut down its plutonium production a couple of times over the past 20 years. Each time, negotiations with the U.S. and North Korea's neighbors broke down and Pyongyang took steps to restart its nuclear program — except this last time.
A Possible Switch To Uranium?
Dan Sneider, a Korea expert at Stanford University's Asia-Pacific Research Center, believes there could be several reasons.
"First of all, the reactor is old and has problems," Sneider says. "Secondly, it may well be that they had decided to move on to uranium enrichment over plutonium as bomb material, and that they had decided ... basically to sell the plutonium reactor for whatever they could get from it, in an international negotiating sense."
Last year, North Korea disclosed that it had developed, secretly, a gas centrifuge facility to enrich uranium. It is not certain whether the facility has enriched any uranium, either highly enriched uranium for bombs or, as the North Koreans assert, low-enriched uranium for reactor fuel.
And then, says Sneider, there is the issue of their work on making a nuclear warhead that could be fitted into the nose cone of a missile.
"This is, I think, the matter of greatest concern for people who are watching the North Korean nuclear program — that is, their progress towards miniaturizing a warhead sufficient to be able to marry it to the ballistic missiles that they're also developing," he says.
New Nuclear Negotiations?
For much of this year, North Korea has not hidden its desire to see international negotiations restart over its nuclear activities. There have been several sets of lower-level talks between U.S. and North Korean diplomats.
The Obama administration has proceeded with extreme caution. Joel Wit says if North Korea now shows as much eagerness for talks as Kim Jong Il did before he died, it could be an early important sign of the new leadership's approach to nuclear bargaining.
"It'll be an early indicator of stability in North Korean policy and also stability in decision-making," Wit says.
At the same time, there's talk that North Korea is planning a long-range missile test, and possibly another underground nuclear test in 2012. That, too, would be an early indicator of where North Korea's nuclear weapons program is headed.