Northeast Asian History Network

Koguryo was founded in the Yalu River basin on a foundation of iron culture. The use of iron spread throughout the middle Yalu River basin after the 3rd century BCE, and multiple tribes of Na congregated in this region. The word “Na” is the root of the modern Korean word for “country” and means “riverside”. The Na tribes were considered to be equivalent to a small country.
In the mid-first century BCE, the various Na tribes in the middle Yalu River basin formed an alliance with the Biryu tribe at its center. As evidenced by the Jumong foundation myth^{[note 001]}, however, the control of the alliance was eventually seized by the Gyeru tribe. The “Records of the Three Kingdoms” recorded that the royal family had changed from the Sonobu to the Gyerubu, indicating that the latter tribe had become the leaders of the alliance.
The process of forming the state of Koguryo was turbulent. The Han dynasty counties in the Liaodong region were absorbed by the Na, and repeated internal conflicts were prevalent within the tribe. At this time, Koguryo's state capital changed from Jolbon Fortress^{[note 002]} to Gungnae Fortress^{[note 003]}. Nevertheless, the Na tribal alliance began to stabilize in the mid-first century after the reign of King Taejo of Koguryo (reign: 53-146 CE^{[note 004]}. A multitude of smaller tribes became integrated into the five major tribes of Koguryo. Thus, the many small tribes united to form the five major tribes described in the excerpt from the above “Records of the Three Kingdoms.” Several Ga, or Jega, made up Koguryo’s ruling class.
Ga, Gan, Han, and Ganji are all synonymous, and they were equivalent to the modern-day use of the word ‘King.’ The word “khan” in Genghis Khan of the Mongol Empire has the same definition. Originally, the term Ga was used to refer to the king of a small country. The word, however, became the name for the ruling class after leaders from the five major tribes became Koguryo court officials.
Nevertheless, the Jega had their own unique powers until the mid-third century. The Jega were divided into Major Ga and Minor Ga depending on the level of influence. As seen in the above excerpt, the Major Ga had government officials, Saja, Joye, and Seonin, rule over their respective branches. As stated in the above record, the list of government officials were reported to the king, indicating that the Major Ga was under his command. In other words, although the Major Ga had a sub-administrative organization of its own, it was part of a system under the control of the king. The king had ultimate power over the military and foreign relations as well. Such powers were integrated into the throne.