The "Song of the Xianbei Brother"(Chinese: 阿幹歌; pinyin: āgān gē) is a popular song of the Xianbei people composed by Murong Wei in 285 AD. It is preserved in Chinese translation and is about the Xianbei chief's regrets for having sent his brother away to the West. The original Chinese translation left the Xianbei word for elder brother (A-kan) in the title, which is identical to the Mongolic word for elder brother (Aqan or Aghan). The same word exists in Turkic and Tungusic languages, but the Xianbei are generally considered Mongolic peoples. This would make the song one of the earliest attestations of a Mongolic language. The song was first translated into English in 1939.
The separation of Tuyuhu from the Murong Xianbei occurred during the Western Jin Dynasty (265-316), which succeeded the Cao Wei (220-265) in northern China. Legends accounted the separation as caused by a fight between Tuyuhu's horses and those of his younger brother, Murong Wei. The actual cause was intense struggle over the Khanate position and disagreement over their future directions. The fraction that supported Murong Wei 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, Tuyuhu 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.