When culture advances overfast and material achievement outruns wisdom, civilization retrogrades and society recedes from high but premature levels to “dark ages” of the interregnum of wisdom. 
Confucius and Lao-tse were eventually deified by their followers in those spiritually dark ages of China which intervened between the decline and perversion of the Taoist faith and the coming of the Buddhist missionaries from India. 
Christianity comatose for 1000 years as a result of an overdose of mysteries and paganism. During so-called European “dark ages” religion became more and more monasticized, asceticized, and legalized. 
Few human rights were recognized in the European Middle Ages; then every man belonged to someone else. The revolt from this error was equally erroneous in that it led to the belief that all men are born equal. 
During these dark ages the territorial state collapsed, and there was a reversion to the small castle groups, the reappearance of the clan and tribal stages of development.  Slavery demands strong regulation and during the European Middle Ages virtually disappeared because the feudal lords could not control the slaves. 
In the same period of time that Europe suffered its “dark ages,” the Islamic world, however, lived through a golden age.