The military history of the Jin dynasty and the Sixteen Kingdoms encompasses the period of Chinese military activities from 266 AD to 420 AD. The Jin dynasty is usually divided into the Western Jin and Eastern Jin in Chinese historiography. Western Jin lasted from its usurpation of Cao Wei in 266 to 316 when the Uprising of the Five Barbarians split the empire and created a number of barbarian states in the north. The Jin court relocated to Jiankang, starting the era of Eastern Jin, which ended in 420 when it was usurped by Liu Yu, who founded the Liu Song dynasty.
The Sixteen Kingdoms were a series of barbarian states occupying northern China after the fall of Western Jin. They were eventually extinguished by Northern Wei in 439 AD.
Organization
The Jin dynasty's military structure was largely inherited from Cao Wei. During the Three Kingdoms period, military leadership was functionally hereditary as long as the successor was loyal to his liege and proved competent. When the commander died, a male member of his family inherited control of his troops, and when a soldier died one of his male relatives inherited his position in the unit. By the end of the Three Kingdoms, the term buqu (部曲) had come to designate the institution of hereditary military leadership. Both bu and qu, meaning battalions and companies, were originally units of military organization during the Han. Under Cao Cao, a more systematic form of hereditary soldiery was implemented through "military families" (士家 shijia) which later became "hereditary troops" (世兵 shibing). As their name implies, able male members born into military families served for life, and when they could no longer serve because of illness or death, their sons or close family members replaced them. Their families lived at the capital and other major centers where they could be used by the government as hostages to ensure the loyalty of their soldiers. They were also forbidden from marrying into non-military families in order to prevent their offspring from exiting the system, thus creating a closed community of military households. Although commoners could still be called up in times of urgent need, the rise of government mandated military communities under Cao Wei and the demobilization of local levies under the Jin dynasty, had by and large, replaced the universal conscription of the Han.
The situation changed after the fall of Western Jin. Having lost the resources of the north, the Eastern Jin army attempted to bolster the number of military families in the south by incorporating convicts, vagrants, and aboriginals. This resulted in a general decline of social status and morale in the military. By the end of the dynasty, military men were regarded little better than government slaves. Terms of service were exceedingly harsh. One in three men from a military family was called upon for a term of service lasting from the age of 15 to their 60s. Essentially their entire life. Those who suffered debilitating injuries had to find a replacement from their family to procure release. Desertion was rampant and exit from the military household system a much sought after reward. By the sixth century the system of hereditary military households had collapsed.
During the following Liu Song dynasty, voluntary recruits began to supplant the defunct military caste system. Many of these soldiers were former members of the previous system who had been freed, and had chosen to re-enlist for better terms, or because they could find no better employment. In practice, many of the military communities which had sprung up during the era of hereditary troops stayed together, and provided the basis for recruitment for the next dynasty.
Equipment
Single mounting stirrups had already been in use since the Han dynasty, but full double stirrups did not appear until the early 4th century AD. A funerary figurine depicting a stirrup dated 302 AD was unearthed from a Western Jin tomb near Changsha. The stirrup depicted is a mounting stirrup, only placed on one side of the horse, and too short for riding. The earliest reliable representation of a full length double sided riding stirrup was also unearthed from a Jin tomb, this time near Nanjing, dated to the Eastern Jin period, 322 AD. The earliest extant double stirrups were discovered in the tomb of a Northern Yan noble, Feng Sufu, who died in 415 AD. Stirrups have also been found in tombs in Goguryeo, a neighboring state outside of Jin dynasty, dating to the 4th and 5th centuries AD, but these do not contain any specific date. The stirrup appeared to be in widespread use across China by AD 477.Hobson, John M. The Eastern Origins of Western Civilisation. Cambridge University Press, 2004, p. 103 ,
The appearance of the stirrup in China coincided with the rise of armoured cavalry, probably as a result of Xianbei influence. Dated to 357 AD, the tomb of Dong Shou shows fully armoured riders as well as horses. By the end of the 4th century murals depicting horse armour covering the entire body were found in tombs as far as Yunnan. References to "iron cavalry" and "iron horse" began to appear at the same time and instances of captured horse armour in numbers as high as 5,000 and 10,000 are recorded. In addition to the stirrups, Feng Sufu's tomb also contained iron plates for lamellar armour. Sources mention the capture of thousands of "armored horses" in a single battle. Armoured heavy cavalry would dominate Chinese warfare from the 4th century AD to the early Tang dynasty when the military transitioned to light cavalry.Dien, Albert. "THE STIRRUP AND ITS EFFECT ON CHINESE MILITARY HISTORY""The invention and influences of stirrup"
Jin Sima Yi
On 11 December, 220, Cao Pi deposed the last Han emperor and proclaimed himself Emperor of Cao Wei. During his reign Cao Pi alienated his brothers Cao Zhang and Cao Zhi. Cao Pi deeply distrusted his close kin and reduced their powers out of suspicion of their loyalty. His brothers and half-brothers were sent away to their nominal fiefs and kept under strict supervision. Moreover Cao Pi regularly interfered in the status of his kin by promoting, demoting, revoking, and restoring their titles at will.
Cao Pi died in 226 and was succeeded by his son Cao Rui. Although Cao Rui was already twenty years old, he was nonetheless appointed a regency council by his father prior to his death. By 237, three members of the regency council had died, leaving only Sima Yi. Sima Yi descended from an old and established family from the Henei Commandery. His brother, Sima Lang, joined Cao Cao early on in his career and Sima Yi followed him in 208. He became a close friend of Cao Pi and joined his entourage in 217. By 224, Sima Yi was left in charge of domestic affairs. Shu Han and Sun Wu continued to pressure Wei. In 233, Zhuge Liang occupied Wudu Commandery but was checked there by Sima Yi and died the following year. In 238, Sima Yi invaded the Gongsun state in the northeast and annexed it. This was followed by a campaign into Goguryeo in 244 and 245 under the leadership of Guanqiu Jian. Cao Rui died in 239 without any offspring of his own and was succeeded by his seven year old adopted son Cao Fang, who fell under the regency of Cao Shuang and Sima Yi.
Cao Shuang and his friends Wang Bi and He Yan were devotees of a mind altering drug known as Five Minerals Powder. Together they headed a movement which sought to dispose of meaningless formalities in society and opposed the traditional doctrines of Confucianism. In 249, in a coup, Sima Yi had Cao Shuang stripped of his positions and shortly thereafter had him and his associates executed; effectively seizing state power in Wei. He died two years later and was succeeded by his son Sima Shi, then 40 years old.
Sima Shi Sima Shi campaigned against Wu and the nomads to the north but achieved no major success against either opponents. Cao Fang tried to retake power for himself in 254 but was pre-emptively attacked by Sima Shi and replaced by his cousin, Cao Mao. In 255 the general Guanqiu Jian rebelled and seized the city of Shouchun. He requested help from Wu, but they were unable to assist him, and the city was retaken by the end of the year. Sima Shi died on 23 March, 255, and was succeeded by his younger brother Sima Zhao.
Sima Zhao In 257 the Wei general Zhuge Dan rebelled in Shouchun, also requesting assistance from Wu, but none was forthcoming. He was defeated in 258. In 260 Cao Mao, like his brother, attempted to seize control of the state, but failed and died in the process. In 264 Sima Zhao conquered Shu Han, eliminating one of the Three Kingdoms, after which he proclaimed himself King of Jin. He died the following year and was succeeded by his son Sima Yan, then 30 years old.
Western Jin On 8 February 266, Sima Yan deposed the last emperor of Wei, Cao Huan, and proclaimed himself Emperor of the Jin dynasty. In contrast to the close guarded suspicion with which Cao Pi treated his kin, Sima Yan immediately enfeoffed 27 of his relatives as princes with autonomy over their fiefs as well as positions in the military and government. The Jin dynasty was in its inception, essentially a family run enterprise.
In the northwestern Qin Province, the Xianbei rebelled under Tufa Shujineng. The Jin sent armies against them twice, in 270 and 271, but were defeated on both occasions. Sensing weakness, the Xiongnu leader Liu Meng also started raiding Jin territory, however he was killed in 272. Tufa Shujineng was defeated in 279 and order was restored to the region.
In the spring of 280, Jin launched an invasion of Wu from the north and west, led by Sima Zhou and Wang Jun respectively. Sun Hao surrendered on 1 May 280 when his troops deserted him, putting an end to the era of the Three Kingdoms.
War of the Eight Princes
Sima Yan, Emperor Wu of Jin, died on 16 May 290, and was succeeded by his son and crown prince Sima Zhong, posthumously Emperor Hui of Jin. Emperor Hui proved to be mentally deficient, possibly even mentally handicapped, and his father was aware of the situation. However he feared that to skip his eldest son in the line of succession would destabilize the empire with a succession struggle, so he maintained Zhong's position as heir apparent. The decision proved to be a disaster. Upon Sima Zhong's accession, the former empress' uncle Yang Jun took regency and removed his rival Sima Liang from power. Emperor Hui's wife Jia Nanfeng organized a coup and removed Yang Jun from power on 23 April 291. With assistance from the empress, the fifth son of Sima Yan, Sima Wei, then killed Liang. The empress Jia Nanfeng turned on Wei and killed him immediately afterwards, becoming de facto ruler of Jin.
In 296 the Di leader Qi Wannian rebelled. He was killed in 299. Another Di leader Yang Maosou set up the state of Chouchi south of Tianshui