Understanding Before 20th Century
Chinese records before the 3rd century BC describe Gija (箕子) as the paternal uncle (or brother in other records) of the last emperor of the Chinese Shang Dynasty, the tyrannical King Zhou, but contain no mention of his relationship with Gojoseon. Gija was imprisoned by the tyrant until the downfall of Shang Kingdom, when King Wu of Zhou released him.
Records written after the 3rd century BC, when China and Gojoseon were at war, add that Gija led 5,000 to east of present-day Beijing, as written in the Geography of Hanshu from Han Dynasty (though some, especially in China, believe him to have moved to present-day Korea), and became the king of Gija Joseon.
Previously, it was widely believed that Gija Joseon was located in present-day Korea, replacing Gojoseon of Dangun. Some scholars today believe that Gija settled west of Gojoseon, based on records from Geography of Hanshu, and Korean record of Samguk Yusa that suggests that Gojoseon continued to coexist with Gija Joseon after the migration of Gija. These scholars believe that Gija's influence was limited to western part of Gojoseon, west of Liao River, as attested by Geographical record of Hanshu that recorded that Gija migrated to the west of Liao River. Furthermore, the record in Samguk Yusa,
Later Dangun moved his capital to Asadal on T'aebaek-san and ruled 1500 years, until king Wu of Chou (ancient Chinese dynasty) placed Kija on the throne (traditional date 1122 BC). When Kija arrived, Tangun moved to Changtang-kyong and then returned to Asadal, where he became a mountain god at the age of 1908. (Ilyon, Samguk Yusa, translated by T. Ha & G. Mintz (1997), Yonsei University Press, p.33)
(御國一千五百年. 周虎{武}王卽位己卯, 封箕子於朝鮮, 壇君乃移於藏唐京, 後還隱於阿斯達爲山神, 壽一千九百八歲),
and the record in Sima Qian's Shi Ji that
King Wu appointed Gija to Joseon, though he was not a vassal (of Zhou)
(於是武王乃封箕子於朝鮮而不臣也).
The Genealogy of the Cheongju Han Clan (청주한씨세보) lists the names of 73 rulers of Gija Joseon and their periods of reign, although not widely accepted by current Korean mainstream historians.
Wiman Joseon is said to begin with the usurpation of the throne from the line of kings descended from Gija.
Read more about this topic: Gija Joseon