Korean believed that ethnically, Korea is a homogeneous country. Korea has very ethnically identical population. While race is a biological classification, ethnicity is a sociological concept. Korean has close blood relation to asian northern nomads. But since Chosun dynasty accepted Confucianism Chosun was affected by Sinocentrism. The spread of Confucianism lead to exclusive and distorted nationalism. But Confucianism have gained a lot of support of confucian scholars and agitated the people with extreme nationalism. Chosun apt to despise to northern nomads. But after Jurchen(northern nomad tribe) conquered to China, Chosun confucianism scholars was chaotic. And the Sino-Japanese war of 1894, Chosun(Korea) abolished Sinocentrism. Nationalism has become a new current of modern history. The rebirth of extreme nationalism has caused terrorism in many countries. Korea is the latest in a line of runaway successes dealing with nationalism. But nationalism tends to make it hard to take a balanced approach to historical events or current geopolitical situations. It is time to seeking measures to reduce negative effects of nationalism and to seeking measures to expand positive effects of nationalism.