The ironic thing about the Korean War is that it was begun (by North Korea) in an attempt to change a status quo that no party involved was particularly satisfied with, in search of an end result that all parties agreed would be ideal (the unification of Korea), and millions of deaths later ended by reestablishing the same static situation it had originate to eliminate. The war was begun, modern perspective tells the historian, because North Korea desperately wanted to reunite the nation under a single "people's government." The irony of the situation is that South Korea also wanted to unite the nation under a single "government of the people" -- the only difference was the question of which regime supported by which superpower should rule the people. North Korea very nearly managed to unite the nation under communist rule within a matter of months, with very little bloodshed, before America intervened to drive the Northern armies back. America's intervention was somewhat unexpected by both Korea and its allies in Russia and China. Equally unexpected was China's later intervention when American/U.N. forces pushed past the former North/South border at the 38th parallel. Yet if one looks closely at theories of international relations such as the ideas presented by defensive realism, one can see that both America's intervention and China's were necessitated by their independent need for security when the balance of power began to shift, and that even a desire for future peace and self-defense can lead to a downward spiral into hostility when war becomes more political than military.
Defensive realism "is an umbrella term for several theories of international politics and foreign policy that build upon Robert Jervis's writings on the security dilemma and to a lesser extent upon Kenneth Waltz's balance-of-power theory (neorealism)." (Beavis) It suggests that security is the primary interest of most states, yet when one state takes action to increase its perceived security this action generally serves to decrease the perceived security of other competing states. This can manifest in numerous ways. For example, some states may feel that the best way to increase their security is through aggression. This aggression may be acquisitive and driven by the need to gain more power and territory so as to build a stronger nation, or it may be punitive and driven by a desire to punish those who would threaten security or national interests in a real or perceived way, or it may be preemptive and either serve to diminish a competitor's ability to attack the nation's interests or serve as a show of strength to deter others from challenging the nation's security. Security concerns may also motivate foreign policy and diplomacy to function in such a way that it causes competing states to feel threatened and in so doing push them into aggression or into building security (which may seem like a building threat). Building armies and weapons which are defensive may seem aggression, and building alliances or widening territory to create a stronger buffer (for security reasons) may also seem or be aggressive. "The security dilemma is an inescapable feature of life in an anarchic environment." (Taliaferro)
Defensive realism not only describes international relations, it also makes recommendations -- however, when looking at history we can see look at the violation of these recommendations in a descriptive way to show where conflict is heightened and prescripted. This theory suggests that states should pursue the most moderate routes to security possible to avoid escalation into war. The strongest states at any given time within an anarchical world order "should pursue military, diplomatic, and foreign economic policies that communicate restraint." (Beavis) In many ways the history of the Korean War is the enactment of these theories and a demonstration of the ways in which history punishes those who do not follow the recommendations of defensive realism.
According to American theories at the beginning of the Korean War, "it seemed close to certain that the [Northern] attack had been mounted, supplied and instigated by the Soviet Union." Tragically, the discovery of more complete records has shown that this was not true. On the contrary, it appears that the Northern movement was driven almost entirely by the wishes of the Korean people and their Northern leader Kim il Sung who had to fight for years to convince Stalin to contribute any sort of aid to his project. Sung's motivation could have been predicted by defensive realism -- he thought of reuniting Korea under Northern rule as the only way to make the North secure from Southern (or American) influence and aggression. He vocalized it to Stalin thus: "The reactionary forces of the South will never agree on a peaceful reunification and will perpetuate the division of the country until they feel themselves strong enough to attack the North." (in: Wingrove) Yet Stalin embraced what would later be formulated as the advice of defensive realism and suggested a more moderate approach that communicated restraint: "If the adversary has aggressive intentions, then sooner or later it will start the aggression. In response to the attack you will have a good opportunity to launch a counterattack. Then your move will be understood and supported by everyone." (in: Wingrove) Eventually, however, Stalin agreed to support North Korea on the condition that Russia would not actively be drawn into the war. His reasons for this are predictable through defensive realism in that he thought it would increase the security of Russia if there was a united communist Korea, and that as long as Soviet support was limited, the security risk would be limited. "Stalin and Mao may have been worried about resurgent Japan and the Prospect of a U.S. military buildup... they needed to gain control of South Korea to secure their position in Northeast Asia. A Communist-controlled Korea would expand the buffer zone on Soviet borders... And divert U.S. attention" (Painter 4-37) Because Russia never did get actively involved in the war, but followed a more moderate course, it was the least injured of the involved nations and in some ways achieved an objective of harming U.S. interests (in causing them to fight a groundless war).
The reason the United States decided to intervene in what would have otherwise been a localized civil war was precisely because of the supposed involvement of Russia in North Korea's movements. "It can be best explained in terms of the 'domino' theory. The U.S. thought that if one of its satellites is given up easily, even without a war, it might provoke the enemy to cause more aggressions, thus, changing the status quo and, in the long run, affecting the balance of power. Thus, now wars have to be fought for strictly political reasons." (Vaidyanatha) This highlights the defensive realism theory of a mutual spiral into aggression, for while Russia was not actually spearheading the attack, the very threat of Russian involvement was enough to drag the U.S. into war. Not only was America afraid of the domino effect by which losing one nation to communism might cause others to fall and upsetting the balance of power (which was somewhat in the favor of America), it also had to deal with security concerns. Theoretically, at least, if the American satellites such as South Korea were overrun, America had less of a buffer against direct attack and less ability to discourage Russia from starting wars of the nuclear and non-nuclear varieties.
Once America got involved, it quickly restored the status quo and pushed the North Korean army back to the 38th parallel. This restored the status quo from before the war. However, General MacAuthor decided to "finish" the war by pushing farther into North Korea to assure the destruction of the North Korean military force. As America pushed its armies into what had originally been North Korean territory, it lost some of its ability to pass as a police action against an aggressive state and began to look like a direct assault on the communist bloc. This was certainly how it appeared to China as the American troops began marching on her borders. Chinese security interests demanded that North Korea serve as some kind of buffer between American forces in South Korea and the Chinese border, and also that American forces not be allowed on Chinese soil. So, as defensive realism would expect, China began to send forces to meet and engage American troops. "When Mao decided to enter the war, it was to 'combat the enemy who dares to advance and attack north of the 38th parallel.'" (Vaidyanatha)
If America had not appeared to be the aggressor, but had stuck strictly to a moderate course that communicated restraint, then it might never have had to face the massive forces of China. However, throughout the war America seemed to act in an unrestrained fashion. For example, when faced with difficult progress through territory that was not always supportive, the American command gave the order that all Koreans (whether Northern or…