The separation of Tuyuhun from the Murong Xianbei occurred during the Western Jin Dynasty (266-316), which succeeded the Cao Wei (220-265) in northern China. Legends accounted the separation as caused by a fight between Tuyuhun's horses and those of his younger brother, Murong Hui. The actual cause was intense struggle over the Khanate position and disagreement over their future directions. The faction that supported Murong Hui for the Khanate position aimed at ruling over China, whereas Tuyuhu intended to preserve the Xianbei culture and lifestyle. The disagreement resulted in Tuyuhu being proclaimed as Khan, or Kehan, and he eventually undertook the long westward journey under the title of the Prince of Jin, or "Jin Wang", followed by other Xianbei and Wuhuan groups. While passing through western Liaoning and Mt. Bai, more Xianbei groups joined them from the Duan, Yuwen, and Bai sections. At the Hetao Plains near Ordos in Inner Mongolia, Tuyuhun Khan led them to reside by Mt. Yin for over thirty years, as the Tuoba Xianbei and Northern Xianbei joined them through political and marriage alliances. After settling down in the northwest, they established the powerful Tuyuhun Kingdom named to his honor as the first Khan who led them there, by subjugating the native peoples who were summarily referred to as the “Qiang” and included more than 100 different and loosely coordinated tribes that did not submitted to each other or any authorities.
After Tuyuhun Khan departed from the northeast, Murong Hui composed an “Older Brother’s Song,” or “the Song of A Gan:” “A Gan” is Chinese transcription of “a ga” for “older brother” in the Xianbei language. The song lamented his sadness and longing for Tuyuhun. Legends accounted that Murong Hui often sang it until he died and the song got spread into central and northwest China. The Murong Xianbei whom he had led successively founded the Former Yan (281-370), Western Yan (384-394), Later Yan (383-407), and Southern Yan (398-410).