BY PATRICK M. CRONIN | APRIL 3, 2013

The Korean Peninsula is on a knife's edge, one fateful step from war. While Koreans are accustomed to periodic spikes in tensions, the risk of renewed hostilities appears higher than at any time in the past 60 years, when American, North Korean, and Chinese generals signed an armistice agreement. Far more than 1 million people died in the Korean War, with at least that many troops and civilians injured over the course of the three-year campaign.

The exact leadership dynamics at play in Pyongyang remain mysterious, but the domestic survival of the Kim family dynasty appears to hinge on maintaining a credible nuclear and missile threat -- backed up by a local great power, China. To achieve the former, Kim Jong Un appears willing to risk the latter. His regime's unrelenting verbal threats are intended to rally domestic support, and its reckless brinksmanship is aimed at forcing the outside world to back down and back off. In the past days and weeks -- adding to the tension created by its recent nuclear and missile tests -- Pyongyang has severed a hotline with Seoul, renounced the 1953 armistice, conducted cyberattacks, and, against its own financial interests, closed down the Kaesong Industrial Complex, which is the only economic thread holding together relations with the South.

There is no single red line that, when crossed, would trigger war, but the potential for miscalculation and escalation is high. North Korea has a penchant for causing international incidents -- in 2010 alone it used a mini-submarine to sink the South Korean naval vessel Cheonan and shelled South Korea's Yeonpyeong Island. The brazen and unprovoked killing of military personnel and civilians shocked many South Koreans, some of whom faulted then-President Lee Myung Bak for a tepid response. The new president, Park Geun Hye (South Korea's "Iron Lady") is determined not to echo that weakness and has vowed a strong response to any direct provocation. Meanwhile, the United States, via the annual Foal Eagle and Key Resolve exercises, has many troops, ships, and planes on maneuvers in the region and, as an additional show of resolve, flew long-range B-2 stealth bombers from Missouri to Korea and dispatched F-22 fighter jets as well.

The desire to show strength, the fear of looking weak, and the presence of tons of hardware provides more than enough tinder that a spark could start a peninsula-wide conflagration. An accident -- such as a straying missile, an incident at sea or in the air, a shooting near the Northern Limit Line or the Demilitarized Zone -- could trigger an action-reaction cycle that could spiral out of control if Pyongyang, running out of threats or low-level provocations, were to gamble on a more daring move. It might calculate that a bold gesture would sow doubt and dissent in South Korea, drive a risk-averse United States to back down and restrain its eager ally, and hand China a fait accompli in which Beijing has no alternative to protecting its upstart neighbor. It might be very wrong.

Let's say that the North decides to fire its new mobile KN-08 intermediate-range ballistic missile, capable of reaching U.S. bases in Guam. An X-band radar based in Japan detects the launch, cueing missile defenses aboard Japanese and U.S. ships. The U.S.S. Stetham, an Arleigh Burke-class destroyer equipped with Aegis phased-array radars, fires its SM-3 missiles, which hit and shatter the KN-08 warhead as it begins its final descent. The successful intercept is immediately touted internationally as a victory, but, now desperate for tactical advantage that will allow it to preserve its nuclear and missile programs, the North Korean leadership orders an assault on South Korean patrol vessels and military fortifications built after the 2010 shelling incident.

The regime feels safe in striking out along the maritime boundary because the two sides have repeatedly skirmished in the area in the past 15 years. But President Park, determined to show backbone, dispatches on-alert F-15K fighter aircraft armed with AGM-84E SLAM-Expanded Response air-to-ground missiles to destroy the North Korean installations responsible for the latest assault. For good measure, they also bomb a North Korean mini-submarine pier as belated payback for the sinking of Cheonan. North Korean soldiers and military officers are killed in the attack. Pyongyang vows a merciless response and launches a risky salvo of rockets into downtown Seoul, in hope of shocking the Blue House into seeking an immediate cessation of fighting. But far from ending the tit-for-tat attacks, North Korean actions have now triggered the Second Korean War.

 U.S. and ROK Combined Forces Command implements a pre-arranged plan -- perhaps using submarine-launched Tomahawk cruise missiles and Massive Ordnance Penetrator bombs dropped from a B-2 -- to eliminate North Korea's two major missile launch facilities: Tonghae in the northeast and Sohae in the northwest, both of which are fairly close to the Chinese border. North Korea responds with more rockets and Scud missiles, accompanied by North Korean Central News announcements suggesting that they could be armed with biological agents. China, seeking to restrain all sides, pours troops and materiel across the border to protect its interests and instigates a secret plan to replace Kim Jong Un with a senior general who understands the North's total dependence on its only ally. The resulting confusion leads to a belief that North Korea, and not just the Kim regime, is collapsing. Meanwhile, the United States quietly embarks on a secret mission to secure North Korea's nuclear weapons.

Even now, however, the Second Korean War has only just begun because, as conflict breaks out, all participants expand their strategic goals. South Korea -- which initially had hoped only to force North Korea to calm down enough to re-enter negotiations on nuclear weapons, expanded inter-Korean economic ties, and human rights -- now believes North Korea is going to collapse and starts to implement an assertive reunification policy. The U.S. policy of deterrence and strategic patience has failed, so Washington decides to pursue active denuclearization and regime change. It joins with Seoul in planning postwar reconstruction in which the peninsula is reunified.

China, which was slow to curb its ally's proliferation and never had a good handle on Kim Jong Un, seeks to ensure that the new leader of North Korea can restore stability. China also wants a new leader in Pyongyang to adopt a pro-China policy -- one which includes continued preferential access to North Korean mineral deposits for its state-owned enterprises. Russia supports China, and it is promised unfettered access to the warm-water port in the Rason Special Economic Zone in northeastern North Korea.

It is easier to start a war than to stop one, but in the best case the Second Korean War might end with an international conference -- perhaps in Jakarta under the auspices of the Association for Southeast Asian Nations -- in which the United States and South Korea come to a modus vivendi with China and a greatly weakened North Korea over the country's future, addressing succession and confederation with the South,  as well as the verified destrcution of nuclear weapons. In the worst case...well, an awful lot more people would die.

The Korean War began in June 1950 as a result of a conscious policy choice on the part of North Korean founder Kim Il Sung. With the Chinese civil war successfully concluded and authoritarianism on the rise, Kim concluded the time was ripe to deliver a knock-out blow and bring a long Korean civil war to a similar conclusion. He spent 10 days amassing 900,000 soldiers near the 38th Parallel, and in the pre-dawn hours on June 25, he ordered the invasion of the South. Hiding in plain sight, the troops nonetheless surprised the Republic of Korea Army, because the presumption was that Kim would never launch a full-scale war that could embroil a war-weary region in another major conflagration.

The presumption, as we know now, was dead wrong. The United States mobilized a formidable international coalition under U.N. auspices and, together with the ROK Army, regrouped and launched their own counteroffensive. American leadership, too, was susceptible to overtly optimistic appraisals. By October, General Douglas MacArthur was so confident of rapid victory that he assured President Harry S Truman that the war would be over by Christmas. But the ferocity of inter-Korean tensions, mixed with Cold War superpower aims, assured the war slogged on until 1953.

The war's renewal would be more likely to result from miscalculation than from deliberate choice. Kim Jong Un may not want war, but amid heightened tensions there are many ways one could start -- and it could well be that it is the United States that miscalculates. There is no sound empirical method for identifying the particular catalyst that would trigger war, but should war begin again in earnest, its intensity and its duration could prove a nasty surprise, as it did the first time. And the consequences could affect Northeast Asia for the rest of the century.