With the death of Kim Jong-il, the hermit state that is North Korea enters the unknown. Kim’s third and youngest son is slated to succeed him but it’s unclear whether the armed forces are prepared to accept his dynastic credentials.

The potential for conflict is high during this period of transition. The military could stage a crisis to prevent Kim Jong-un from assuming control if the Great Successor — as he’s been dubbed by state media — doesn’t provoke a confrontation with the South and the United States himself in the process of consolidating power.

North Korea’s regime makes a habit out of staging international crises in order to bolster its legitimacy at home. Last year alone, the North sank a South Korean corvette and bombarded a disputed island along the maritime border. Its nuclear program flies in the face of international sanctions which have done little to change the North’s behavior.

Roughly a quarter of the country’s annual economic output is devoted to defense. More than a million North Koreans are employed by the military. South Korea’s armed forces, by contrast, claim 4 percent of gross domestic product (although its economy is estimated to be more than two hundred times the size of the North’s) and it has 650,000 personnel in employ. In sheer numbers, including artillery, fighter planes and warships, the North’s army is nearly twice the size of the South’s. But in terms of logistics and technology, the South’s is far more sophisticated.

North Korea’s leaders may hope that nuclear weapons give them an edge over their rivals. If they could threaten to obliterate the capital city of Seoul, which is situated just forty kilometers from the demilitarized zone, with a single strike, it should deter American and Japanese intervention in the event of renewed hostilities. But this capacity is theoretical at best, given the difficulties that have plagued the North Korean ballistic missile program.

The calculation is also misguided in that the United States, a nuclear power itself, would probably not be deterred from intervening if Pyongyang threatens to use atomic weapons. But if North Korean leaders believe otherwise, it might induce them to start a war. The stated aim of keeping the country on a perpetual war footing, after all, is to eventually reunify the peninsula on the North’s terms.

Even if nuclear weapons aren’t deployed, Seoul could be leveled under a barrage of artillery charges, potentially with hundreds of thousands of casualties. On the North’s side of the demilitarized zone are stationed hundreds of Soviet-made tactical ballistic missiles, capable of delivering chemical agents, along with thousands of artillery pieces in hardened dugouts that can fire up to 500,000s rounds per hour. More than 70 percent of the North’s military manpower is stationed on the border. Tunnels are known to have been dug to facilitate an invasion.

Before North Korean tanks could start rolling south, the allied powers, certainly the United States, would have picked up on troop movements and prepared countermeasures. Airstrikes against North Korean armor, artillery and military infrastructure would commence before an invasion could even be attempted.

North Korea’s air defenses are dense but obsolete. The Americans could probably fly stealth bombers from Guam without difficulty. The defense systems around Pyongyang are hardened but immobile, making them easy targets for bombardment. Other, purely military targets could be subject to cruise missile strikes launched from American destroyers and submarines in the Pacific Ocean.

The generals in North Korea will be forced to implement their plans with haste if they aren’t to lose the war before it properly began. Artillery along the demilitarized zone would open fire on South Korean defensive lines and Seoul, setting off a flood of refugees that would frustrate the South’s ability to stage an immediate and effective defense.

After suffering heavy casualties while clearing the massive minefields that line the demilitarized zone on both sides, Northern troops would seek to overrun the South’s defenses within a matter of weeks, before American reinforcements could arrive. This is unlikely to succeed. Southern troops should be able to stave off a North Korean invasion while allied support pours in from Japan and across the Pacific.

The only option left to North Korea at that point to tip the balance in its favor would be to deploy tactical nuclear weapons. Its mechanized divisions are no match for the superior South Korean tanks and what’s left of its air force after American bombardments will not turn the tide of the war. North Korea’s nuclear devices are few and primitive, however, while their use could prompt the United States to deploy nuclear weapons of their own, devastating the North Korean state.

The allies should be able to stop the Northern offensive, perhaps in less than two weeks, but that wouldn’t be the end of it. American reinforcements and South Korean reserves would have to be called on to defeat the North. On their march to Pyongyang, they would likely encounter fierce resistance from army remnants and citizen militias. North Korean’s mountainous terrain is unfavorable to an invasion. On the allied side, the heaviest military casualties could be incurred during this phase when questions could start to be raised in the West about the need to reunify the peninsula.

It’s also at this time that China could seek to involve itself. It cannot tolerate an American bulwark on the Manchurian border. If South Korea and the United States push for regime change in Pyongyang, that is unlikely to sit well in Beijing where there may be no intention of aiding the North Koreans in a war of aggression but where there is still sympathy for the other communist state.

China wouldn’t seek a direct confrontation with the allies but could move in forces of its own to contain the disorder, stem a North Korean refugee tide and signal to the world that it will not allow a reunification of the peninsula on anyone’s terms but its own.

Whatever China’s intentions, there would be a real threat of escalation if it, too, became part of the conflict. The risk of confrontation — accidental or staged by renegades — would remain high until the two powers agreed on an outcome.

A Second Korean War, one that doesn’t morph into a Sino-American conflict, would be costly in blood and treasure. When war seemed likely in 1994, it was estimated (PDF) that in the first ninety days of skirmishes, more than 50,000 American military personnel could be killed and wounded along with nearly ten times as many casualties on the South Korean side. Those numbers probably need to be revised downward, given the improvements in American and South Korean defense technologies. But they could rise exponentially if the North does go nuclear.