Chapter Eleven is titled, "The Worlds of Islam", but a better title might be, Islam takes over the World.  It seems incredible that a religion could spread so wide and so fast as Islam was able to do from 600-1500. The length and breadth of the Islamic culture and religion was referred to by Strayer as, "the first truly Global Civilization".  Act locally, and think globally would have summed up the vast civilizations and peoples that converted to Islam.  Again, I am intrigued by the practical reasons that peoples and cultures chose to follow certain religions, and to switch allegiances if the need arose, like the arrival of a conquering Army.  It makes sense that if a giant empire/civilization/culture is roaring across continents like Islam did in Afro-Eurasia, that your choice would be to get on the bus or be run over by it. On the other hand it sounds like people joined willingly, many feeling a comfort from the monotheistic teachings that were prominent in Judaism, and Christianity, Strayer referred to it as a "social conversion, the movement from one religiously defined social community to another".  Islam was indeed a religiously defined social community with its teachings of correct behavior, versus the emphasis in Christianity on correct beliefs.  I think this emphasis on correct behavior in regard to all aspects of ones life, including political, social, religious, and personal, made Islam a unifying force for these diverse peoples spread from as far away as Spain, on through North and West Africa all the way to India. This unifying force became a global network for the exchange of ideas, goods, and technologies that brought about a surge in science, medicine, philosophy, and Islamic scholarship.  The reach of Islam and its tenets of correct behavior resonate today with adherents all over the world, including America.