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 to 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, that of native chieftains were hereditary (shixi 世襲) and were not endowed with an official salary.
The most powerful chieftains were appointed heads of area commands (dudufu 都督府), while less prestigious posts were head 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 not only accepted the suzerainty to the Chinese government, but also paid tributes (gongfu 貢賦). Yet there were never fix quotas for tributes (actually a special form of taxes) tied to the number of households or the population size. The geographical chapter of the official dynastic history Jiutangshu 舊唐書 (40 Dili zhi 地理志) lists 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, and some were abolished and new ones created, and sometimes regular prefectures were transformed 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 regions with a large amount of "foreign" people which had migrated from the northwest into China proper. After the Chinese dynasties had lost the north and northeast, the jimi system was applied to regions in China proper where "aboriginal" people lived. During the Yuan period 元 (1279-1368), the jimi system was standardized, and the native chieftains given the title tusi 土司.