Why has modern Korean history proven to be tumultuous?
In the most modern sense, one can look at the long term division of Korea produced by the Post-World War II era and the Cold War, in that it led to the formation of long term military style dictatorships on both sides of the 38th parallel.
For many years after World War II and the Korean War, South Korea was led by a virtual dictator, or at the least the military and government had much more power over individuals, and civil rights were severely limited.
In North Korea, of course, a family dynasty was established that has led to a cult of personality for its current leader, Kim Jong il, and his father before him, Kim il-Sung. Their harsh and repressive rule, along with massive poverty, border clashes, and a new nuclear program has led to a very tumultuous half century for the Korean Peninsula.
The geographic location and relatively small size of Korea has placed it at a tremendous disadvantage in the scheme of world events. In nineteenth and early twentieth century geopolitics, Korea sat at the nexus between the major Asian powers—China, Japan, and Russia. As these giants sought to expand their respective spheres of influence in Asia, Korean soil became a natural battleground due to its strategic location. During the Cold War period, a divided Korea became the boundary between the Soviet Union and the United States. In virtually all of Korea’s many modern conflicts, the Korean people have had external events shape their nation’s destiny and have become pawns in much larger geopolitical games.
Korea’s internal affairs, however, have also shaped the road trodden. Korea’s willingness to depend on Chinese support and defense meant that it did not formulate a coherent or effective foreign policy until the Western powers and Japan had already become far too powerful to deal with on an equal basis. Korea’s early and rigid rejection of the West and exceptionally conservative court served the same purpose: wasting valuable time hoping that the foreigners would disappear. By the time the court realized their hopes were in vain, they had lost the opportunity for initiative.
Korea was in the way of the japanese imperial policy and later in the zone of interest of too many superpowers - USA , USSR and China with their opposing ideologies. Also the effects of the Cold War were felt after separation, by the lack of communication between the two parts of the same country and because of the arms race. Later ideological indoctrination and the leaders mentalities made impossible an effective approach. Korea's situation is similar with many European nations covered by the influence of the different allies after WW2 .The main problem is that, once created the political and military structures, they are very hard to be changed, whithout the loss of many innocent lives .