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.