Background

In 258, the Tuoba chieftain, Tuoba Liwei led his people to occupy the abandoned Han dynasty city of Shengle in Yunzhong Commandery. He became a vassal to the Cao Wei and its successor, Western Jin and subjugated neighbouring tribes to expand his power. The Jin, fearing the Tuoba's growing influence, sowed discord among the tribe's chieftains to weaken them. After Tuoba Luguan became chieftain in 294, he decided to split the Tuoba domain into west, central and east between him and his nephews. The split lasted a decade before the western Tuoba chieftain, Tuoba Yilu, reunified them in 307.

At the time, the Western Jin was undergoing the upheaval of the Five Barbarians. The Xiongnu of Shanxi established the Han-Zhao state and posed a threat to the Jin in northern China. The earliest involvement of the Tuoba in the conflict was in 304, when the central and western Tuoba provided reinforcements to Jin against the Han. It was not until after Tuoba Yilu's reunification that they took a more active role in supporting Jin. In 310, Tuoba Yilu aided the Jin Inspector of Bing province, Liu Kun, to quell the rebellion of the Tiefu-Xiongnu chieftain, Liu Hu.

Reign of Tuoba Yilu

Tuoba Yilu and Liu Kun became sworn brothers, and as reward for helping him, Liu Kun petitioned the Jin court to bestow Yilu the title of Duke of Dai. The Tuoba became a vital fighting force for Jin in their war against Han, with Liu Kun being almost entirely dependent on their military strength. Shortly after attaining his fief, Yilu forced Liu Kun to grant him five counties north of the mountain ranges. In 312, after Liu Kun lost his capital, Jinyang, Yilu sent his forces to successfully reclaim it for him. For his services, the Jin court elevated Yilu's title to Prince of Dai and allowed him to grant offices to his subordinates in 315.

Yilu showed preference towards his younger son, Tuoba Biyan (拓跋比延), which upset his older son, Tuoba Liuxiu (拓跋六脩). In 316, after Liuxiu refused to take orders from his father, Yilu led his troops to attack him but was killed in battle. Dai was thrown into a state of confusion, with its people suspecting and killing one another or fleeing the state. Yilu's nephew, Tuoba Pugen killed Liuxiu and proclaimed himself the new Prince of Dai, but he was unable to quickly resolve the crisis.

Period of instability

Tuoba Pugen died shortly after, and while his unnamed son succeeded him, he too would die later that same year. Therefore, the chieftains acclaimed his cousin, Tuoba Yulü as the new prince. During his reign, Yulü further weakened the Tiefu and expanded his territory by conquering the former lands of the Wusun in the west and the lands west of the Mohe people in the east. However, in 321, he was assassinated by Pugen's widow, Lady Qi, who installed her son, Tuoba Heru to the throne.

As regent, Lady Qi submitted to the Later Zhao dynasty, whose people referred to Dai at the time as a "queendom" (女國). Heru began exercising power in 324 and moved the capital to Mount Dongmugen (東木根山; northwest of present-day Xinghe County, Inner Mongolia), but he soon died in 325 and was succeeded by his brother, Tuoba Hena. In 327, threatened by Later Zhao, Hena shifted the capital again to Daning. Throughout his rule, Hena's claim to the throne was challenged by Tuoba Yihuai, Tuoba Yulü's son who had escaped the aftermath of his father's death and went into exile. In 329, Hena fled to the Yuwen tribe after the Dai chiefs replaced him with Yihuai, but in 335, he was welcomed back and reinstated as Yihuai lost support. Yihuai fled to the Later Zhao, and in 337, he returned to Dai with an army and reclaimed the throne at Shengle.

Reign of Tuoba Shiyijian

Before his death in 338, Tuoba Yihuai ordered his chieftains to welcome back his brother, Tuoba Shiyijian, who was hostage in Later Zhao, and acclaim him as the new prince. Many of them preferred his other brother, Tuoba Gu (拓跋孤), but Gu personally went to Zhao and brought Shiyijian back to Dai. Shiyijian ascended the throne north of Fanji (繁畤; in present-day Fanshi County, Shanxi), and he willingly split his domain with Tuoba Gu.

During Shiyijian's reign, the Dai enjoyed a lengthy period of prosperity and reached its peak. Shiyijian set up various new offices to handle separate administrative duties and codified the law. His territory supposedly spanned from the Yemaek in the east to the Fergana in the west, and from the Yin Mountains in the south to the northern edge of the desert. Shiyijian had an army of 100,000 strong, and in 340, he moved the capital back to Shengle. He entered into a marriage alliance with the Former Yan, though relations were tense at times, leading to clashes between the two sides.

Throughout his rule, he also had to deal with the Tiefu tribe, who vacillated between fealty and hostility towards Dai. Shiyijian repeatedly defeated the Tiefu, but in 376, their chieftain, Liu Weichen persuaded the Former Qin to launch a campaign against Dai. During the campaign, Tuoba Jin (拓跋斤), the son of Tuoba Gu who resented that he did have the same power as his father after his death, had Shiyijian and many of his sons assassinated. Former Qin capitalized on the confusion and captured Yunzhong, thus ending the Dai.

Former Qin treated the defeated Tuoba clan kindly, and he allowed Shiyijian's grandson, Tuoba Gui to live with the Dugu tribe in the old Dai territory. In 386, taking advantage of Former Qin's rapid decline that followed the Battle of Fei River, Tuoba Gui restored his family's state. Though he initially claimed the Prince of Dai title, he changed it to Prince of Wei later that year, and his state would become known in history as the Northern Wei.