Chapter 5: Three Kingdoms Era

About the middle of the third century AD, the Chinese threat began to serve as a unifying political force among the loose confederations of tribes in the southern part of the Korean peninsula. Adopting the Chinese political system as a model, the tribes eventually merged into two kingdoms, thereby increasing their chances of survival against Chinese expansionism. Geographic features of the southern parts of the peninsula, in particular the configuration of mountain ranges, caused two kingdoms to emerge rather than one. The two kingdoms eventually came to play an important role in Korean history.

In the central part of Korea, the main mountain range, the Taebaek Range, runs north to south along the edge of the Sea of Japan, which lies off the east coast of the peninsula. However, approximately three-fourths of the way down the peninsula, at about the thirty-seventh parallel, the mountain range veers southwest, dividing the peninsula almost in the middle. This extension is called the Sobaek Range. Tribes west of it were not shielded by any natural barriers against the Chinese-occupied portion of the peninsula, whereas, those to the southeast were protected. Moreover, the presence of the mountains prevented the tribes in the two regions from establishing close contacts. These two regions began to develop into separate entities.