During the Cao Wei era, the Southern Xiongnu were split apart by stratagems on the northern grasslands. Wuhuan warriors were recruited into the State of Wei's cavalry and lost to the last man fighting the Han Army. The Wuhuan tribes gradually declined in the north.
The former overlords of the grasslands had fallen at the hands of the Central Plains dynasties. The Xianbei filled the void they left behind.
The Kebineng tribe of the Xianbei, which lived near the frontier passes, had long been influenced by advanced Han culture. Its strength gradually surpassed that of the other Xianbei tribes. Seizing the historic opportunity presented by the Han Army's destruction of Wei, Kebineng unified the Xianbei and was acclaimed as their chieftain.
In the fifth year of Jianxing (236), Grand Tutor and Grand Marshal Lan Tian was "murdered." Zhuge Liang and Lan Yuan began purging the Great Han court. Kebineng immediately took advantage of the chaos, joining forces with the two small states of Goguryeo and Buyeo to invade Liaodong, which had only recently been pacified. He aimed to seize its people, livestock, and wealth.
Liaodong was a bitterly cold region with few troops stationed there. In addition to organizing the garrison's resistance, Governor Chen Dao sent messengers by both land and sea to seek aid from the Central Plains.
Renewed fighting on the northeastern frontier underscored the need for a "military superpower," directly accelerating the political purge led by Zhuge Liang and Lan Yuan.
In the summer of the sixth year of Jianxing, General of Chariots and Cavalry Guan Ping, General Who Guards the North Wei Yan, and General Who Pacifies Bandits Lan Ji led three armies totaling eighty thousand troops to relieve Liaodong and punish the foreign tribes. Liu Bei's old acquaintance and former Wei general Tian Yu served