North Korea's newly minted leader presents the U.S. and its allies with an even more unknown character than his recently deceased father _ and the strategic challenge of dealing with an inexperienced young man who sits on a nuclear arms program, a stash of chemical weapons and the world's fourth-largest army.
At the tender age of 27, give or take a year or two, Kim Jong Un is poised to become the world's youngest commander in chief. With virtually no track record, he will be learning on the job. From a military perspective, which takes "know your enemy" as its cardinal rule, that makes him a huge wild card as he sorts out his potentially thorny inheritance.
While the transition could offer an opportunity for positive change, this week's announcement of North Korean leader Kim Jong Il's death immediately set off alarms in situation rooms from Seoul to Washington.
The younger Kim is said to have graduated from Kim Il Sung Military University and was suddenly promoted to four-star general last year in the first promotion hinting that he was being groomed to succeed Kim Jong Il, his father. Otherwise, Kim has little public record of military service. Until just before the announcement of his father's death, he had never even issued an order, according to South Korean media.
In Pyongyang, Kim Jong Un is credited with orchestrating an artillery attack on Yeonpyeong Island that killed four South Koreans in November 2010. However, the South Korean reports say his first directive was for troops to stop training and return to their bases.
"Worries are high," said Baek Seung-joo of the state-run Korea Institute for Defense Analyses in South Korea. "Kim Jong Un is too young, and it's possible that elite generals' loyalty to him may grow thin in the long run."
Even so, all signs from Pyongyang indicate Kim has garnered enough support from the cabal of generals his father left behind to become the public face of the regime. Whether he will lead or follow, or eventually be cast aside, is another question.
"Where the guessing really starts is in determining who the power, or powers, behind the throne will be _ who will be whispering in his ear and to whom he will be listening," said Ralph Cossa of the Pacific Forum of the Center for Strategic and International Studies, a private think tank. "The military remains a power behind the throne, but just how powerful and who speaks for the military are still not clear."
Although Pentagon spokesmen said Thursday the transition appeared to be going smoothly, troops around the region are on heightened alert.
South Korea has ordered its military to step up surveillance of the Demilitarized Zone that has separated the two countries since their 1950-53 war. Japan called an emergency meeting of its Cabinet and put its coast guard on alert. President Barack Obama vowed the U.S. would stand by its allies, and Taiwan suspended regular missile and artillery tests to avoid causing "inappropriate speculations."
Such jitters are warranted.
When Kim Jong Il assumed power after the death of his father in 1994, he elevated the North Korean military with him, lavishing funds on the army, pursuing the expensive development of ballistic missiles and stubbornly refusing to abandon his dream of building nuclear weapons even as his nation slipped deeper into poverty and isolation.
The policy is called "songun" _ military first _ and Kim used it masterfully to befuddle his enemies at home and abroad. But it has also created a symbiotic relationship that may prove hard for Kim Jong Un to sustain.
By some estimates, as much as a third of North Korea's state-run economy is set aside for its military. An estimated 1.2 million troops are on active duty and 7.7 million in reserves, out of a total population of only 24 million.
Service is a lifelong process. Children are pressured to enter youth guard organizations. When troops leave active duty, they usually join paramilitary reserve forces, where some remain until they are in their 60s, according to Joseph Bermudez, a North Korea military analyst for the London-based Jane's Information Group.
"The military is everything in North Korea," said Toshimitsu Shigemura, a North Korea expert at Waseda University in Tokyo. "It has the absolute power that comes ahead of everything. Kim Jong Un will have to keep that in place to get support for his leadership."
Under Kim Jong Il, North Korea acquired enough weapons-grade plutonium to build several atomic bombs. The North's nuclear program has made it an international pariah, though experts question whether it can make nuclear bombs small enough to deploy on a warhead, a key to using them in any conflict.
But North Korea has repeatedly proven it is capable of using its conventional forces, which could be the more dangerous threat during the leadership transition.
It is suspected of using a minisubmarine to attack and sink a South Korean corvette in March last year, killing 46 sailors in the deadliest encounter between the two countries since their war. North Korea denies involvement.
Eight months later, it fired the volley of shells at Yeonpyeong Island.
The attacks underscore what is perhaps North Korea's greatest military strength: its willingness to make provocative moves, often with the diplomatic goal of gaining concessions, and gamble that its adversaries will not risk war by responding with full force.
That attitude is key because the North's military is by no means invincible. Its navy is antiquated, its air force is mostly obsolete and fuel for training is scarce.
Still, it has a 2-to-1 advantage over the South in tanks, long-range artillery and armored personnel carriers, according to the U.S. State Department. It has a huge reserve of special forces _ 200,000 commandos by South Korean estimates _ ready to slip across the border to carry out assassinations and cause havoc at air bases and ports critical to the South's defense.
North Korea also has 2,500 to 5,000 tons of chemical weapons stored across the country, according to South Korea's Defense Ministry, which believes the North is also capable of cultivating and manufacturing anthrax bacteria, smallpox viruses and cholera viruses for biological warfare.
Seoul, South Korea's capital and a city of more than 10 million, lies only 30 miles (50 kilometers) from the border, within reach of many of the North's 13,600 long-range artillery guns.
A repeat of 1950, when North Korean forces streamed across the border in a surprise attack that sparked the Korean War, is hard to imagine. South Korea's 650,000 troops are much better prepared than six decades ago, and are backed up by 28,500 American troops and another 50,000 in nearby Japan. U.S. F-16 fighters based in Japan could be over North Korea is less than an hour.
Skirmishes are a more likely scenario.
Many North Korea experts believe the two incidents in 2010 were intended to bolster the reputation of Kim Jong Un, and he could be under pressure to orchestrate another attack in the months ahead to demonstrate his credibility as a hawkish figure, like his father.
But Cossa, the analyst at the Center for Strategic and International Studies, suggested Kim and the military leadership will be too busy working out their new pecking order to pick fights elsewhere.
"There is rampant speculation that the new leadership will have to establish its bona fides by doing something aggressive," he said. "My guess is that this would be the best time for the respective militaries to enjoy Christmas leave. The odds that the new leadership would do something provocative during the mourning period or during the transition period that follows seem particularly low."