An extensive study is made by the author on the system of Suzerain Supervision & Protection (SSP)implemented in the rural grass-roots n eighborhood unions during the period of the Northern & Southern Dynasties(N.Wei: 386-534A.D.;W.& E.Jin:265-420A.D.).According to the study,the historical backgro unds and conditions for the rise of this system consist of two aspects:on one ha nd,the mass population migration had deprived the rural neighborhood unions of t heir function in ruling the residents.On the other hand,with the rapid enforceme nt of the feudal relationship known as`Shelter & Dependency',emerged in great nu mber those fort-lords who,with economic and clan domination,had established mili tary self-defense organizations such as castles,fortresses,strongholds as well a s fortified walls.As a result,a large number of residents who tried to evade the disasters of war were kept under control by the fort-lords.The author affirms t hat the SSP system started in the late Western Jin rather than,as generally beli eved,in the early N.Wei.This system lasted nearly two centuries.Even after Xiaow en the Emperor of the N.Wei abolished the SSP system and carried out the system of `Three Top-officials in Charge',the clan-masters and fort-lords still surviv ed and continued to exert their influence on such affairs as clan power control, winning over the sheltered and dependent people,and monopolization of some regio nal political power.