U.S. strategy changed in 1950, when the North Koreans invaded the South, sparking the Korean War. Pyongyang's motives remain unclear, as do the roles of Moscow and Beijing in the decision. Obviously, Pyongyang wanted to unite the peninsula under communist control, and obviously, it did not carry out its invasion against Chinese and Russian wishes, but it appears all involved estimated the operation was within the capabilities of the North Korean army. Had the North Korean military faced only South Korean forces, they would have been right. They clearly miscalculated the American intent to intervene, though it is not clear that even the Americans understood their intent prior to the intervention. However, once the North Koreans moved south, President Harry Truman decided to intervene. His reasoning had less to do with Korea than with the impact of a communist military success on coalition partners elsewhere. The U.S. global strategy depended on Washington's ability to convince its partners that it would come to their aid if they were invaded. Strategic considerations aside, not intervening would have created a crisis of confidence, or so was the concern. Therefore, the United States intervened.
After serious difficulties, the United States managed to push the North Korean forces back into the North and pursue them almost to the Yalu River, which divides Korea and China. This forced a strategic decision on China. The Chinese were unclear on the American intent but did not underestimate American power. North Korea had represented a buffer between U.S. allies and northeastern China (and a similar buffer for the Soviets to protect their maritime territories). The Chinese intervened in the war, pushing the Americans back from the Yalu and suffering huge casualties in the process. The Americans regrouped, pushed back and a stalemate was achieved roughly along the former border and the current Demilitarized Zone. The truce was negotiated and the United States left forces in Korea, the successors of which President Obama addressed during his visit.
The great mystery of the post-Cold War world is the survival of the North Korean regime. With a dynamic South, a non-Communist Russia and a China committed to good economic relations with the West, it would appear that the North Korean regime would have found it difficult to survive. This was compounded by severe economic problems (precipitated by the withdrawal of economic support from the Chinese and the Russians) and reported famines in the 1990s. But survive it did, and that survival is rooted in the geopolitics of the Cold War.
From the Chinese point of view, North Korea served the same function in the 1990s as it did in 1950: It was a buffer zone between the now economically powerful South Koreans (and the U.S. military) and Manchuria. The Russians were, as during the Korean War, interested in but not obsessed by the Korean situation, the more so as Russia shifted most of its attention west. The United States was concerned that a collapse in North Korea would trigger tensions with the Chinese and undermine the stability of its ally, South Korea. And the South Koreans were hesitant to undertake any actions that might trigger a response from North Korean artillery within range of Seoul, where a large portion of South Korea's population, government, industry and financial interests reside. In addition, they were concerned that a collapsing North would create a massive economic crisis in the South, having watched the difficulties of German integration and recognizing the even wider economic and social gap between the two Koreas.
In a real sense, no one outside of North Korea was interested in changing the borders of the peninsula. The same calculations that had created the division in the first place and maintained it during and after the Korean War remained intact. Everyone either had a reason to want to maintain an independent North Korea (even with a communist regime) or was not eager to risk a change in the status quo.
The most difficult question to answer is not how the United States viewed the potential destabilization of North Korea but rather its willingness to maintain a significant troop level in South Korea. The reason for intervening in the first place was murky. The U.S. military presence between 1953 and 1991 was intended to maintain the status quo during the Cold War. The willingness to remain beyond that is more complex.
Part of it simply had to do with inertia. Just as U.S. troops remain in Germany a generation after the end of the Cold War, it was easier not to reconsider U.S. strategy in Korea than to endure the internal stress of reconsidering it. Obviously, the United States did not want tensions between South Korea and North Korea, or to have the North Koreans misunderstand a withdrawal as an invitation to try another military move on the South, however unlikely. The Japanese saw Korean unification as problematic to their interests, since it could create a nearby industrial economic power of more than 70 million people and rekindle old rivalries. And North Korea, it would seem, actually welcomes the American presence, believing it limits South Korean adventurism. Between inertia and what we will call a proto-strategy, the United States remains.
With the loss of its Cold War patrons and the changing dynamic of the post-Cold War world, the North Koreans developed a survival strategy that Stratfor identified in the 1990s. The Koreans' intention was to appear -- simultaneously -- weak, fearsome and crazy. This was not an easy strategy to carry out, but they have carried it out well. First, they made certain that they were perceived to be always on the verge of internal collapse and thus not a direct threat to anyone but themselves. They went out of their way to emphasize their economic problems, particularly the famines in the 1990s. They wanted no one to think they were intent on being an aggressor unless provoked severely.
Second, they wanted to appear to be fearsome. This would at first blush seem to contradict the impression of weakness, but they managed it brilliantly by perpetually reminding the world that they were close to developing nuclear weapons and longer-range missiles. Recognizing that the Americans and Japanese had a reflexive obsession with nuclear weapons, Pyongyang constantly made it appear that they were capable of developing nuclear weapons but were not yet there. Not being there yet meant that no one had to do something about the weapons. Being close to developing them meant that it was dangerous to provoke them. Even North Korea's two nuclear tests have, intentionally or incidentally, appeared sub-par, leaving its neighbors able to doubt the technological prowess of the "Hermit Kingdom."
The final piece was to appear crazy, or crazy enough that when pressed, they would choose the suicide option of striking with a nuclear weapon, if they had one. This was critical because a rational actor possessing one or a few weapons would not think of striking its neighbors, since the U.S. counterstrike would annihilate the North Korean regime. The threat wouldn't work if North Korea was considered rational, but, if it was irrational, the North Korean deterrence strategy could work. It would force everyone to be ultra-cautious in dealing with North Korea, lest North Korea do something quite mad. South Korean and U.S. propaganda did more for North Korea's image of unpredictability than the North could have hoped.
North Korea, then, has spent more than two decades cultivating the image to the outside world of a nation on the verge of internal economic collapse (even while internally emphasizing its strength in the face of external threats). At the same time, the country has appeared to be on the verge of being a nuclear power -- one ruled by potential lunatics. The net result was that the major powers, particularly South Korea, the United States and Japan, went out of their way to avoid provoking the North. In addition, these three powers were prepared to bribe North Korea to stop undertaking nuclear and missile development. Several times, they bribed the North with money or food to stop building weapons, and each time the North took the money and then resumed their program, quite ostentatiously, so as to cause maximum notice and restore the vision of the weak, fearsome lunatic.
The North was so good at playing this game that it maneuvered itself into a position in which it sat as an equal with the United States, Japan, Russia, China and South Korea -- and it would frequently refuse to attend the six-party talks. The ability to maneuver itself into a position equal to these powers was North Korea's greatest achievement, and it had a tremendous effect on stabilizing the regime by reinforcing its legitimacy internally and its power externally. Underneath this was the fact that no one was all that eager to see North Korea collapse, particularly since it was crazy and might have nuclear weapons. North Korea created a superb strategy for regime preservation in a very hostile region -- or one that appeared hostile to the North Koreans.
Crucially for Pyongyang, North Korea was of tremendous use to one power: China. Even more than North Korea's role as a buffer state, its antics allowed China to emerge as mediator between the inscrutable Pyongyang and the frustrated United States. As China's economy grew, its political and military interests and reach expanded, leading to numerous tensions with the United States. But Beijing recognized that North Korea was a particular obsession of the United States because of its potential nuclear weapons and American sensitivity to weapons of mass destruction. Whenever North Korea did something outrageous, the United States would turn to China to address the problem. Having solved it, it was then inappropriate for Washington to press China on any other issue, at least for a while. Therefore, North Korea was a superb mechanism for the Chinese to deflect U.S. pressure on other issues.
For all of their occasional provocations, the North Koreans have been careful never to cross a line with conventional or nuclear power to compel a response from the South or the United States. Their ability to calibrate their provocations has been striking, even as their actions have escalated through nuclear tests to military action against South Korean ships and islands in the West Sea. Also striking is the manner in which those provocations have increased China's leverage with the United States.
At this point, it would be difficult for the United States to withdraw from South Korea. The North Korean nuclear threat fixes the situation in place, even for troops that aren't relevant to that threat. The troops could be withdrawn, but they won't be because the inertia of the situation makes it easier to leave them there than withdraw. As for the South Koreans, they simultaneously dislike the American presence and want it there, since it ensures U.S. military involvement in any crisis.
While the U.S. troop presence in Korea may not make the most sense in a global U.S. military strategy, it ironically seems to fit, at least for now, the interests of the Chinese, South Koreans and Japanese, and even in some sense the North Koreans. The United States, as the global power, therefore is locked into a deployment that does not match the regional requirements, requires endless explanation and is the source of frequent political complications. What we are left with is a U.S. strategy not based necessarily on the current situation but one tied to a historical legacy, left in place by inertia and held in place by the North Korean nuclear "threat."