The route from regensburg in modern germany to constantinople wa:
factor accounts for the popularity of this particular route?
the route followed a large and major river.
the route went through several populated areas.
the route avoided the rocky mediterranean coast.
the route followed flat land useful for soldiers.

to protest slavery i would think it would be a

cultural history is your answer

islamic religious leaders have traditionally been people who, as part of the clerisy, mosque, or government, performed a prominent role within their community or nation. however, in the modern contexts of muslims minorities in non-muslim countries as well as secularised muslim states like turkey, indonesia and bangladesh, religious leadership may take a variety of non-formal shapes.

compared to religious leaders/clerics of the other abrahamic faiths, islamic clergy are said to resemble rabbis and not priests. unlike catholic priests they do not "serve as intermediaries between mankind and god",[1] have "process of ordination",[2] or "sacramental functions",[1] but instead serve as "exemplars, teachers, judges, and community leaders," providing religious rules to the pious on "even the most minor and private" matters.[1]