Demobilization and War of the Eight Princes During the early days of the Western Jin, the imperial Sima family began allowing their princes to assume the roles of military governors, a privilege that was non-existent under the preceding
Cao Wei dynasty. Following the
unification of the
Three Kingdoms in 280,
Emperor Wu of Jin also issued orders for the demobilization of every province and commandery in the empire, and reduced the military authority of the provincial inspector into a civilian role. Only 100 military officials were stationed in large commanderies, while smaller commaderies only had 50. The policy of concentrating military power in the hands of the princes was intended to safeguard the dynasty from potential usurpers and keep the power of the gentry clans in check. However, this decision became a contributing factor to the
War of the Eight Princes (291–306); after the death of Emperor Wu, he was succeeded by his eldest son,
Emperor Hui of Jin, who was
developmentally disabled. With the emperor a mere figurehead in his own court, the princes instead pitted their armies against one another for real control over the empire. As the Jin military weakened itself under the princes, many counties and commaderies were left defenceless to rebellions. In the finals years of the Western Jin, tribal subjects collectively known as the
Five Barbarians started to dominate northern and western China; they were known as the
Xiongnu,
Jie,
Xianbei,
Di and
Qiang.
The Five Divisions and hu of Bing province The migration of the nomadic people into the Chinese interior had been ongoing since the early
Han dynasty. In 50 CE, after the Xiongnu empire was divided into two, the
Southern Xiongnu became a vassal state for the Han on the northern frontier within the
Great Wall. The chanyu's court was moved to
Xihe Commandery in
Bing province while his followers served as auxiliaries in defending the border commanderies from nomadic forces such as the Northern Xiongnu and
Xianbei. However, their relation with the Han remained tense due to the poor living conditions on the frontiers and the Chinese court interfering in their politics. They thus frequently rebelled, eventually exiling their chanyu and dissolving his government in 189, just as the Han was experiencing their
own collapse. In 216, the warlord,
Cao Cao, detained the chanyu,
Huchuquan in at
Ye and reorganized what remained of the Southern Xiongnu into the Five Divisions in central
Shanxi. Though the Xiongnu eroded as a unified identity, Bing remained home to a myriad of "
hu" tribes. The Five Divisions was soon dominated by the
Chuge branch, and during the
Jiaping era (249–254), their leader,
Liu Bao unified the divisions, which prompted the Wei-Jin courts to intervene. They were gradually divided back into five, and their nobles including Liu Bao had to send their children as hostages to the Chinese capital,
Luoyang. Through these arrangements, the Five Divisions underwent a significant degree of
sinicization and were even allowed to hold Jin offices, but resentment against the ruling dynasty persisted. As the noble,
Liu Xuan, states in the
Book of Jin: The
hu tribes excluded from the Five Divisions often intermingled with those from other ethnic group. A notable example was the
Tiefu tribe, whose descendants were Xiongnu who mixed with the
Xianbei. The
Jie were also among the miscellaneous
hu peoples in Bing. Their exact origins is still debated by scholars today, although one of their chieftains,
Shi Le, was a descendant of a Southern Xiongnu tribe, the Qiangqu. When a great famine broke out in 303, many of the Jie and
hu became displaced. The Chinese provincial inspector, looking to fund his own military, had these tribesmen captured and sold them into slavery, scattering them around
Hebei and
Shandong.
Ethnic tensions in Guanzhong The term "
Qiang" broadly referred to groups of pastoral nomads in the western regions of modern day
Gansu and
Qinghai. Since the Western Han period, many of the Qiang submitted to the Chinese court and were allowed to settle in the
Guanzhong region and the watersheds of the
Wei and
Jing rivers. There, they worked as farmers alongside Chinese settlers, but many were also turned into slaves for local magnates. Due to the oppression they faced, the Qiang often instigated large-scale rebellions which adversely affected the Han military and economy. Living close to the Qiang were the
Di tribes, who became tributaries as the Han expanded westwards and annexed their land. The
fall of Han and the
Three Kingdoms period further encouraged the immigration of nomadic people to repopulate devastated areas and provide military power and labour. The Guanzhong region in particular became a contested region between warlords and later between the states of
Cao Wei and
Shu Han. In 219, Cao Cao relocated around 50,000 Di from Wudu to
Tianshui and
Fufeng commanderies. The Qiang and Di people were numerous in northwestern China, and they fought for Wei or Shu depending on their circumstances. Other tribal people who resided in the northwest included the
Lushuihu and
Xiuchu, along with newly-migrated Xianbei tribes such as the
Tufa and
Qifu. By the late 3rd century, the tribes made up around half of the population in Guanzhong. While Wei kept the tribes mostly under control, the northwest descended into chaos under the Western Jin as their governors struggled to keep the support of the tribes. In 270, the Xianbei chieftain,
Tufa Shujineng, led a
multi-ethnic rebellion against Jin in
Liang and
Qin provinces that lasted until 279, with the rebels briefly taking control over Liang. From 296 to 299, the tribes rebelled again, this time acclaiming the Di chieftain,
Qi Wannian as their emperor. Qi Wannian's rebellion was accompanied by famines and plagues so severe that it devastated the Guanzhong and prompted tens of thousands of refugees to move into
Hanzhong and
Sichuan in search of food. The rebellious tribes of Guanzhong and Bing province raised concern among a few officials within the Jin court. After the unification in 280, the minister Guo Qin (郭欽), advised Emperor Wu to focus on moving the tribal peoples out of the borders. Following Qi Wannian's defeat in 299, another minister,
Jiang Tong, submitted an essay titled
Xi Rong Lun (徙戎論; Discussion on Relocating the Rong Tribe) to the court, also calling for the tribes' repatriation. However, both proposals were rejected.
Xianbei migration and alliances with Jin During the 2nd century, the Xianbei people supplanted the Xiongnu on the northern steppe and, unified under the confederation of
Tanshihuai, launched numerous raids on the Han's borders. However, after Tanshihuai's death in 181, the confederation went into an immediate decline due to a succession crisis. Many of the Xianbei tribes seceded and decided to migrate southward with the intention of settling down near or within the Chinese interior. In the northeast, where the
Wuhuan people once dominated before their defeat at the
Battle of White Wolf Mountain, the Xianbei
Murong,
Duan and
Yuwen tribes came to fill in the power vacuum that was left. The Murong was the first of the three to attach themselves to the
Central Plains dynasties by aiding the
Cao Wei in their
campaign against
Gongsun Yuan. They remained affiliated well after the founding of Jin, and despite a war between both sides from 281 to 289, the Murong resubmitted to Jin and their chieftain,
Murong Hui, was appointed Commander of the Xianbei. Meanwhile, in 258, another Xianbei tribe, the
Tuoba, occupied the abandoned city of
Shengle north of
Shanxi, also becoming a vassal of Wei and Jin. The Xianbei retained most of their nomadic way of life and rendered their services as skilled horsemen. In the midst of the War of the Eight Princes, the Chief Controller of
You province,
Wang Jun, sought to consolidate his control over his domain. He allied himself with the surrounding Duan, Yuwen and Wuhuan, who provided him with cavalry units who fought in the campaigns against
Sima Ying and
Sima Yong. The Xianbei were a deciding factor in
Sima Yue's victory in the civil war, but they also carried out the brutal sackings of
Ye in 304 and
Chang'an in 306. Their military effectiveness encouraged the Jin to continue employing them in containing the growing threat of
Han-Zhao, with the Tuoba soon joining on the side of Jin as well.
Climate Change Modern historians and meteorologists believe that
climate change was an important factor in the migration of nomadic peoples into the Chinese interior, as the weather became too cold and dry in the north for agriculture.
Chu Coching stated that there was a cold period from the
Three Kingdoms to the
Northern and Southern dynasties, with relevant historical records reporting cases of extreme weather phenomena, such as the freezings of the
Huai River in 226 and the
Bohai Sea in 336. Research conducted in the
Mu Us Desert also found that
desertification took place around the steppe between the Han and
Tang dynasties, making it difficult for cities to survive. There was a severe decline in population; the Han census in 157 was 56.5 million people and 10.7 million household, but Jin census in 280 was only 16 million people and 2.5 million households. The cold and dry weathers prompted Chinese farmers to move to the warmer southlands and steppe peoples to move into northern China for fertile land. During the
Taikang era (280–289), the Jin accepted a series of submissions from people claiming to be "Xiongnu" living outside the border, with the largest group coming in 286, purportedly at 100,000. Natural disasters and famines became common occurrences and were aggravated by the War of the Eight Princes. == Rise of Cheng-Han ==