The "loose reins" system (jimi 羈縻) was an indirect mode of administration carried out in the northwestern, northern and southwestern borderlands. Native rulers or chieftains were endowed with a Chinese title and thus worked as officials for the Chinese government. The social and political structure of the tribes thus indirectly governed was not altered. The idea behind this method was "to check the barbarians by barbarian [methods]" (yi yi zhi yi 以夷治夷).
The system was created during the Tang period 唐 (618-907) and was in use still in the early decades of the Republican period (1912-1949). Native chieftains were officially appointed into a position corresponding to their political power. Accordingly, they were formally invested into the nominal position of a commander-in-chief (dudu 都督), regional inspector (cishi 刺史), or so, and were given a seal and all rights of an imperial official (including the obligation to participate each year in a court audience in the capital), yet in contrast to the regular posts, these of native chieftains were hereditary (shixi 世襲) and were not given an official salary.
The most powerful ones were appointed heads of area commands (dudufu 都督府), and less prestigious posts were heads of indirectly administered prefectures (jimifu 羈縻府, jimizhou 羈縻州, also called fanzhou 蕃州 "barbarian prefectures" or bianzhou 邊州 "border prefectures", in contrast to zhengzhou 正州 "regular prefectures"), districts (jimixian 羈縻縣) or settlements (jimitong 羈縻峒).
In that way the Chinese government was able to forestall revolts, saved administrative cost, and enlarged (at least nominally) the extent of the empire. Native chieftains paid not only loyalty to the Chinese government, but also tributes (gongfu 貢賦), yet there was never fix quota tied to the number of households or so, nor did the central government expect the tribes to be paid in an annual turn. Yet these were not regularly demanded. The geographic treatise of the official dynastic history Jiutangshu 舊唐書 gives a total number of 107 jimifu and 638 jimizhou, or 856 indirectly administered territories of all types. In the course of time the names of these administrative units were often changed, some were abolished, others created, and sometimes regular prefectures transferred into indirectly administrated ones, and vice versa.
During the Song period 宋 (960-1279) there were also indirectly administrated units in central China, mainly in the remote mountainous regions, where natives tribes were settled. The term qiaofanzhou 僑蕃州 was applied to region with a large amount of foreign people which had migrated from the northwest into China proper. Having lost the north and northeast, the jimi system was applied to regions where aboriginal people lived. During the Yuan period 元 (1279-1368) the jimi system was regularized, and the native chieftains were called tusi 土司.