When Islam arose and spread in the first half of the 600s B.C.E. it encountered a majority Christian population and also many Jews in the areas it conquered. Islam granted these people a special status called dhimmi, meaning protected.
Those neither Christian nor Jewish were at first given the option of conversion to Islam or the sword — forced conversion. But in the course of time, Islam treated all non-Muslims as dhimmis.
The main features of dhimmi status were a special tax imposed on all adult males and, in turn, exclusion from political office and exemption from military service (likely because of distrust of a dhimmi’s loyalty or patriotism). In its early years, Islam imposed other requirements upon dhimmis, including forbidding them to ride camels or horses, permitting them only donkeys. It also required distinctive clothing for public identification. Christians were allowed the use of things forbidden to Muslims — pork and alcoholic beverages, provided they didn’t flaunt such use.
Dhimmi law continued the pre-Islamic Arab treatment of slaves, who were protected by their superiors as long as they remained subservient and loyal to their clan or tribe. In that respect Muslims brought along a practice from their pagan past even though they stated that this pre-Islamic era had been a time of ignorance and barbarism.
Dhimmitude also, however, followed an arrangement existing in Byzantine law that formulators of shari’a law likely knew about.
Some discussions of dhimmitude (the status of dhimmis) suggest that it was an early form of minority rights, and Christians soon became a minority in territories ruled by Islam. Christians, like Jews, had the right to live according to their own laws — canon law for Christians and halakha law for Jews. Disputes in these communities usually got settled in Christian or Jewish courts.