Kochoson was the first country formed in Korea and was based on the Bronze culture. Kochoson was established in 2333 B.C., and the Laioning district was its center. Kochoson gradually rose as a center of the East. Around the 4th century B.C., it struggled for power with Yen China. It thrived and occupied many of the surrounding territories. In 108 B.C, Kochoson was defeated by Han China. The people of Kochoson scattered out in all directions and spread the Iron culture to all parts of the Korean peninsula. With the downfall of Kochoson, the nations of Puyo, Koguryo, and the three Hans were formed. They used iron to make farm implements that increased productivity. By then, agriculture was highly developed, military power was stronger, and social developments and changes accelerated.

In the north, the nations Puyo, Koguryo, Okcho, and Tong'ye developed. Puyo grew around the Sungari River basins in Manchuria, Koguryo rose in the environs of the mid-Amnokgang (Yalu) river, Okcho stood in the plains of Hamhung on the eastern coast, and Tong'ye developed to the south. Out of all the northern nations, Koguryo conquered all of them.