Private armies (buqu 部曲, jiabing 家兵) were common among the nobility during the Wei 曹魏 (220-265), Jin 晉 (265-420), and Southern and Northern Dynasties 南北朝 (300~600) periods. During the Tang period 唐 (618-907), the word buqu denoted serfs (jiapu 家僕).
The original meaning of the word buqu, as it was used during the Han period 漢 (206 BCE-220 CE), was "regiment". A General-in-chief (da jiangjun 大將軍) used to have the command over five divisions, which were divided into regiments. The creation of private armies began during the reign of the usurper Wang Mang 王莽 (r. 8-23 CE), when landowners from among the distinguished families (haoqiang 豪強, haomen 豪門) began protecting themselves against groups of bandits. The disintegration of state power made such steps necessary. These private armies consisted of family members and their retainers (binke 賓客) and serfs. They were only created for ad-hoc purposes and not meant as a permanent means of defense. In the late decades of the Eastern Han period 東漢 (25-220 CE), when the central government likewise lost its monopoly of power, the local nobility again initiated means to defend their property against marauding bands of landless peasants and sectarian movements like the Yellow Turbans (Huangjin 黃巾). This time, the private armies consisted mostly of peasants who sought shelter by a landowner, but also of client-farmers (dianke 佃客), retainers (mensheng 門生) and subordinates in office (guli 故吏).
While political disturbances were only short during the Wang Mang interregnum, prospects for peace and security were less brilliant in the early 3rd century. Magnates therefore decided to be prepared for future cases of conflicts and retained the institution of private armies. The troops worked as farmers in times of peace, but could immediately turn into soldiers, should there be the need for. This procedure was similar to that of troops on the military agro-colonies (tuntian 屯田) which were founded by the government all over the country in order to revive the economy. In these colonies, soldiers worked as farmers when no military engagement was expected. The expression "official regiments" (guan buqu 官部曲) was therefore also used for troops of the colonies.
In the empire of Wu 吳 (222-280) in southeast China, another similarity between private armies and government troops can be seen. The house of Sun 孫 made the office of general hereditary, and the troops subordinated to this office thus were in fact "private" troops of that general. Some of the Sixteen Barbarian states 十六國 (300~430), like the Cheng-Han 成漢 (304-347) state in Sichuan, made their generals responsible for the recruitment and payment of their troops. General Fan Changsheng 范長生 (d. 318) therefore was allowed to collect taxes and recruit troops on the base of household registers (huji 戶籍).
During the Southern and Northern Dynasties period, the status of private troops was relatively low, and they were socially ranked as "have-nots" (jiankou 賤口) who did not enjoy the full range of "civil" rights. A documents from the Northern Zhou period 北周 (557-581) even shows that buqu troops had more or less the status of serfs, but had more freedom than slaves (nubi 奴婢). Emperor Wu 北周武帝 (r. 560-578) ordered in 577 to free all war captives the Western Wei 西魏 and Northern Qi 北齊 (550-577) had made. Originally free persons were to become free people (minwu 民伍) again, but dependent persons (jiu zhuren you xu gong ju 舊主人猶須共居), males and females, were to be brought back to their masters, the males as buqu soldiers, the females as servants (kenü 客女).
The legal code Tanglü 唐律 from the Tang period also includes a similar paragraphs, in which buqu persons were allowed to own private belongings, but were still members of their master's household. Slaves, buqu persons and females were not taxed under the Sui 隋 (581-618) and Tang dynasties because they did not own land. This social status was inheritable. If the master freed a buqu person, the latter was handed over a document to proof his status as a free person. Tang period documents on buqu persons are scarce, and the term disappears thereafter.