Why did Korea pursue a policy of isolation?

I won't give you a complete answer. I will say that you should broaden your question a bit. Korea was not alone in NE Asia trying to keep out outsiders. Japan was isolated as a matter of policy from Westerners from about the time of the institution of the Tokugawa Shogunate. It feared being taken over, with Western Catholic missionaries being seen by the Japanese as a dangerous foreign presence. The government of Japan also feared the Japanese converts to Catholicism. Korea was similar to Japan in its attitude towards foreigners, but more so. The Korean elites' foreign policy was to 1. Placate China 2. Conduct very tightly controlled trade with Japan (through Tsushima)[END] for many years during the Yi Dynasty. The Chinese also tried to keep foreign contacts to a minimum---especially the Ming. The Mongols, Yuan Dynasty, were much more open to foreign contacts than the native Chinese, the Han, were. What I want to say, is that ALL three NE Asian countries shared a very similar isolating impulse, and narrowing your ';intelligible unit'; down to merely Korea will lead you into making some warped conclusions---all fiery Korean nationalists to the contrary, NE Asian history should be studied as a unit.Why did Korea pursue a policy of isolation?
Historically Korea has been isolated from the rest of East Asia by water and mountains. Korea has also prided itself on being fiercely independent. While allowing cultural exchanges with China and Japan, Korea has fought hard to maintain its political sovereignty for thousands of years. So, really, the policy of isolation has a lot to do with how Korea formed geographically apart from the rest of East Asia.