Baojia 保甲 was a system of communal self-defense created during the Song period 宋 (960-1279) and revived during the Republican era (1912-1949). It was a specialization of the lijia system 里甲 used for local self-administration. Emperor Shenzong 宋神宗 (r. 1067-1085), inspired by the reformer Wang Anshi 王安石, initiated the system as the "law on security groups" (baojiafa 保甲法) and ordered that each ten household were to build a security group (bao 保), fifty a large security group (dabao 大保) and five hundred a superior security group (dubao 都保). The first was headed by a headman (baozhang 保長), the second by a great headman (da baozhang 大保長), and the third a superior head and a vice superior head (dubaozheng 都保正, fubaozheng 副保正). Each household with more than two male adults was to provide one security guard (baoding 保丁), in yet in later times the numbers were reduced to one security guard for five households, with one security group for 25 households, and one superior security group for 250 households. In their leisure time, when no agricultural work was required, the "strongmen" (caiyong 材勇) of each village were trained. The security group exercised police powers, organized night watches and were responsible for arresting delinquents.
The aim of this system was twofold. On the one hand, the security system relieved the local government of administrative duties. The members of each security group cared for the proper registration of their households, mutually observed each other (an old method called lianzuofa 連坐法), and in addition to that organized the defense of the village community. In that way, the security system was a kind of local militia taking over duties normally carried out by military garrisons. For this purpose, the members of the security groups were trained in martial arts, and those around the capital in Kaifeng 開封 (today in Henan province) obtained regular military training, at least in the initial years of the system, to support the regular military. The main effect of the system was that government expenditure for local security decreased. Instead of the government dispatching troops or paying policing forces, the local population itself was responsible for law in order in their own district. During the reign of Emperor Zhezong 宋哲宗 (r. 1085-1100) the military training of the security guards was abolished.
The system remained in used throught the end of the Qing dynasty and was in 1932 revived by Chiang Kai-shek 蔣介石 in the provinces of Henan, Hubei and Anhui. Terminology and organization differed from the traditional system. Each household provided one household head (huzhang 戶長), ten households constituted one tithing (jia 甲), headed by a tithing head (jiazhang 甲長). Ten tithings were one security group (bao) headed by a security head (baozhang), residing in a local security office (jiaban gongchu 甲辦公處). From 1934 on the system was extended to all cities under the jurisdiction of the Kuomintang 國民黨, and in 1937 in all provinces. The government issued statues for the security groups (Baojia tiaoli 保甲條例). The main purpose was that the population mutually took an eye on each other and so prevented the formation of "rebellions". The measure was part of Chiang's strategy of encircling and destroying (weijiao 圍剿) Communist groups. The security groups worked according to four aspects, namely administration and observation (guan 管), political indoctrination (jiao 教), taxation (yang 養, lit. "nourishment") and safeguarding (wei 衛). During the Sino-Japanese war the system was intensified, and the security groups were politicized (danghua 黨化, with a Guomingdang representative in each group), transformed into virtual police groups (jingchahua 警察化), obtained special privileges (tewuhua 特務化) and in the end were made para-military units (junshihua 軍事化). The groups were of course disbanded in 1949.