One of the more surreal experiences available to someone living in the year 2016 is to wake up in Seoul—home of K-Pop, Gangnam style, and a growing collection of attractive postmodern skyscrapers built with the accumulated wealth of the last few decades—and then travel up the highway to the North Korean border. This doesn't take long. If Seoul were Washington, D.C., the ironically named demilitarized zone would be substantially closer than the city of Baltimore, or, to go in the other direction, roughly as far away as Manassas. That's about 25 miles.
Since Kim Jong Un's military is better equipped than was the Confederacy's, a journey to the border can thus seem disconcertingly short. After you pass the fortifications along the Han River (down which agents of the North have frequently attempted to infiltrate the Seoul region) and arrive at the DMZ itself, it is possible with binoculars to stare directly into the North Korean city of Kaesong. As the North keeps what is visible from observation posts in the South relatively spic-and-span, the nature of hell is slow to reveal itself. You may not immediately notice, for example, that the mountains north of the border are almost entirely denuded. The locals have cut down the trees for firewood.
Concealed in that deforested terrain is Kim Jong Un's substantial number of long range artillery pieces, capable of throwing something like 7,000 rounds per hour into Seoul during the early stages of renewed fighting. You can't say "early stages of a war" in this context because the war, as a matter of law, has been ongoing since 1950, with only a military armistice keeping the peace between 1953 and the present. There are no efficient defensive measures to stop such a barrage—only the time-consuming business of counterfire, airstrikes, and seizing terrain north of the border while hoping the North runs out of ammunition.
There is no military scenario that does not involve the near-destruction of Seoul, one of the largest cities in the world. There is also no scenario in which the United States is not totally involved. In addition to the nearly 30,000 troops we have based there, one interesting detail of the U.S.-South Korea relationship, unknown to most Americans, is that in the event of resumed hostilities with the North all South Korean forces fall under the operational control of an American four-star general—a consequence of the United States wanting to maximize control over the volatile anticommunist Syngman Rhee during the early days of the alliance.
It remains the position of the South Korean government to seek peaceful reunification with the North. To make two blisteringly obvious observations: It is difficult to see how this will come to pass without the collapse of the Kim regime, and thus difficult to see how it will be in any way "peaceful." Contributing to the difficulty of making predictions is the role that would be played by China during the reunification of the peninsula. China remains the North's only friend, and for years it has been resisting calls to reduce the economic cooperation that makes the Kim family's war machine possible. Especially in the nationalist climate of today's Chinese politics, Beijing would not simply recline and watch as South Korea and its American ally occupied the North in the event of a regime collapse there.
This fact brings us to an essential point about South Korea's delicate strategic position in the wider Pacific, and helps explain why the government of President Park Geun Hye is somewhat more reticent about the belligerence of Xi's China than, say, the government of Japan's Shinzo Abe. South Korea needs America in order to survive, but it needs China for unification. If Beijing fears that the peninsula is about to be stitched together on terms it finds contrary to its own interests, it is very likely to intervene. It has done so before.
Indeed, in recent years Park has made an effort to take her country closer to China, going as far as to attend a military review in Tiananmen Square where she stood next to Xi and Vladimir Putin. It now appears that Xi botched this opening, or at least decided it wasn't worth the cost. In return for her photo op on the parade stand, Park got a cold Chinese shoulder after new North Korean nuclear tests, and furious protests from Beijing when she continued to work on bringing a sophisticated American missile defense system to her country. These events, combined with the now multi-generational security alliance and cultural ties between Seoul and Washington, mean that South Korea remains firmly tied to the United States.
This is good news for China hawks who want South Korea's help in resisting Xi's aggressiveness. But it doesn't change the fundamental strategic calculus. The North Korean threat and the dream of unification always will loom larger for Seoul than any sort of common cause with other nations on China's periphery, like Japan. Moreover, there is no Pacific NATO to stitch together the operations and strategic decision-making of American allies, nor anything close to it. This "hub-and-spoke" arrangement that depends upon Washington's coordination was arguably advantageous in the 1950s when it was established. But today it does little to allay tensions between these Pacific allies—tension that Xi is delighted to exploit.
If the politics of 2016 have reinforced any lesson of history for Americans, it is that things are often stable right up until they are not. This applies to the North Korean regime, which could last another twenty years, or only twenty months. But it also applies to America's relationships with its Pacific friends, all of which have interests of their own, politics of their own (looking at you, Philippines), and have to survive near a wealthy and increasingly hostile great power. Whatever the substantial difficulties, it is long past time to start building a Pacific alliance system that looks more like what contained, and ultimately defeated, the Soviet Union in Europe.