The military history of the Three Kingdoms period encompasses roughly a century's worth of prolonged warfare and disorder in Chinese history. After the assassination of General-in-chief He Jin in September 189, the administrative structures of the Han government became increasingly irrelevant. By the time of death of Cao Cao, the most successful warlord of North China, in 220, the Han empire was divided between the three rival states of Cao Wei, Shu Han and Eastern Wu. Due to the ensuing turmoil, the competing powers of the Three Kingdoms era found no shortage of willing recruits for their armies, although press-ganging as well as forcible enlistment of prisoners from defeated armies still occurred. Following four centuries of rule under the Han dynasty, the Three Kingdoms brought about a new era of conflict in China that shifted institutions in favor of a more permanent and selective system of military recruitment. This ultimately included the creation of a hereditary military class as well as increasing reliance on non-Chinese cavalry forces and the end of universal conscription.
Organization
Recruitment and organization As the Han dynasty fell into disarray after the Yellow Turban Rebellion, its system of conscription and checks on military leadership broke down, giving local leaders the autonomy to recruit their own personal armies. At the heart of each army was a group of trusted Companions (親近 qinjin) consisting of family members, close friends and clansmen hired by whatever means was available to their lord. Cao Cao's earliest commanders who formed the nucleus of his army were all clansmen (Cao Xiu, Cao Zhen, Cao Chun). There was no need for conscription as the conflicts of the late Han dynasty created willing recruits who sought protection under a strong army. This type of soldier, characterized by a lack of loyalty to state or nation, primarily concerned with survival, made up the majority of the army outside of the leader's close following. Due to the lack of loyalty among common troops, acts of heroism and courage were particularly emphasized among commanders who were expected to lead from the front. A typical example of this type of commander would be Dian Wei, a former local bully noted for his great strength, appetite, and his choice of weaponry, two halberds of immense weight, who served under Cao Cao. In 195, he personally led a group of volunteers clad in double armour (兩鎧 liang kai) against Lü Bu's forces while his liege made his escape. He was promoted to colonel of the bodyguard unit known as the Tiger Warriors and later met his death against Zhang Xiu in 197. While echoes of Han organization continued through the formal titles of military structure, in effect the wars of the Three Kingdoms were fought between armies of bands led by individuals selected by dint of violence and charisma.
Training Military training programs for the general populace in the inner provinces were mostly discontinued after 30 AD to reduce the risk of rebellion. The total number of professional soldiers in standing armies in the Eastern Han, including all the smaller groups, amounted to approximately 20,000 soldiers. Expeditions and campaigns relied upon tens of thousands of troops from local militia armies and non-Chinese auxiliaries, supplemented by professional and semi-professional troops. The men in the inner provinces of the empire could be called to serve during emergencies or serve in local militias to fight against bandits, but these men received no formal training or regular exercise. On the other hand, men of the frontier provinces were liable for conscription and military service as before. This had a negative impact on the performance of the Han army, as noted by Ying Shao, who remarked that "sending [such] men into battle without training is just throwing them away". The majority of soldiers recruited during the early stages of the Three Kingdoms period were thus "neither disciplined nor well trained in the use of arms". Formations and drill still existed, but these were the exceptions rather than the norm, and there is no evidence of troops engaging in a regular training system or large scale exercises. Most commanders favored simple rather than complex formations and maneuvers. An example of a formation and drill that did exist is Zhuge Liang's Eight Formation Plan, which included different configurations named after Heaven, Earth, Wind, and Clouds. It is not clear what these designations mean, but the Eight Formation Plan was traditionally a square formation composed of nine divisions in three sections, used extensively by Zhuge Liang during his northern expeditions as well as for military training. The lack of training severely constrained the kind of orders a commander could give for his troops to follow. As a consequence of the limited tactical flexibility at their disposal, the majority of battles were carried out in one of two ways: a head on charge by elite shock troops followed by the loosely organized army of incoherent and disparately trained and equipped soldiers, or ambush and surprise the enemy before they could even respond and cause them to rout.
The training that the privileged elite received was far greater in extent compared to that of the common soldier. For example, Cao Cao's son, Cao Pi, started his military education in early childhood. He began training in archery at the age of five, started learning how to ride a horse at the age of six, and could both ride and shoot a target at a hundred paces by the time he was eight. Horse archery was also practiced in Shu Han, which fielded a "Flying Army" of mounted archers.
Hereditary troops In contrast to the military hierarchy of the Han dynasty, leadership of a unit in the Three Kingdoms was functionally hereditary as long as the successor was loyal to his liege and proved militarily 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.
Tuntian Tuntian, often rendered as "[military] agricultural colonies," were self-sustaining farming communities created for the purpose of providing food for the military. Generally consisting of displaced peoples, refugees, and bandits, tenants of a tuntian were expected to protect themselves in times of emergencies and in return were exempt from corvée labour. Unlike the tuntian system of the Han dynasty, which was generally hands off, the tuntian policy of the Three Kingdoms era was to directly provide them with supplies and material assistance. The policy of tuntian was implemented primarily by Cao Cao, Tao Qian, and Gongsun Zan.
Equipment
Armies of the Three Kingdoms era used largely the same equipment as the Han dynasty since it directly follows the end of the Han. There were however some minor differences and developments such as the increasing prevalence of armoured cavalry. In one battle, the warlord Cao Cao boasted that with only ten sets of horse armour he had faced an enemy with three hundred sets. The horse armour may however have just been partial frontal barding. Mounting stirrups were already in use, possibly as early as the Han dynasty, but full riding stirrups would not appear until the 4th century. References to "dark armour" (xuan kai or xuan jia 玄鎧/玄甲) and "brilliant armour" also began to appear in the 3rd century. This is probably in reference to the association of high quality steel with black ferrous material.
Weapons were largely the same as well, although there was more focus on idiosyncratic weapons wielded by particularly noteworthy individuals. For example, one man named Chen An apparently wielded a great sword over two meters in length and Sun Quan's wife had over a hundred female attendants armed with daos. Trends in warfare that had already been underway during the Eastern Han continued to gain momentum. By the end of the Three Kingdoms, the single edged dao, with its thicker and more durable dull side, had overtaken the straight double-edged jian as the primary close combat weapon. The more expensive, lighter, and less durable jian entered the domain of court dancers, officials, and expert warriors. While halberds were still used during the period, long spears and lances (similar to pikes) re-rose in prominence over halberds for infantry and cavalry forces. This was believed to have been the result of the long spear and lances' simpler construction, the adoption of long spears and lances by heavy cavalry to strike infantrymen, and the adoption of tighter infantry formations with less room for swinging and hooking [of halberds] in response to the greater threat by cavalry. Soldiers in the northeast specialized in long spears.(魏書曰：議者多言「關西兵彊，習長矛，非精選前鋒，則不可以當也」。公謂諸將曰：「戰在我，非在賊也。賊雖習長矛，將使不得以刺，諸君但觀之耳。」) Wei Shu annotation in Sanguozhi vol. 1. After the Han dynasty, the crossbow gradually faded in importance until it made a mild resurgence during the Tang dynasty, under which the ideal expeditionary army of 20,000 included 2,200 archers and 2,000 crossbowmen.
References to "great shields" occur in their usage on the front line to protect spearmen and crossbowmen. Shields were also commonly paired with the single edged dao and used among cavalrymen. Descriptions of the Battle of Guandu mention that Cao Cao's soldiers employed shield cover above their heads each time they moved out into the open due to oppressive arrow fire from Yuan Shao's wooden towers.
Although Zhuge Liang is often credited with the invention of the repeating crossbow, this is actually due to a mistranslation confusing it with the multiple bolt crossbow. The source actually says Zhuge invented a multiple bolt crossbow that could shoot ten iron bolts simultaneously, each 20 cm long.
Dark armour A report in 231 AD mentions the capture of 5,000 suits of "dark armour" (xuan kai or xuan jia 玄鎧/玄甲) and 3,100 crossbows. Dark armour appears in Han texts as well, but only as the attire worn by honor guards at funeral processions. The only known trait about dark armour is that it reflected the sun's rays. This probably means dark armour was made of high-quality steel, which was often associated with black ferrous material.
Brilliant armour Cao Zhi mentioned three different kinds of armour, two of which were variants of "brilliant" armour:
Brilliant armour was made of decarburized steel, which shines blue-black when polished, giving it its name. Chen Lin described brilliant armour in the following manner:
Wheel catapult