In its earliest centuries, the rapid spread of Islam had been accompanied by the creation of an immense Arab Empire, very much in the tradition of earlier Mediterranean and Middle Eastern empires. By the tenth century, however, little political unity remained, and in 1258 even the powerless symbol of that earlier unity vanished as Mongol forces sacked Baghdad and killed the last Abbasid caliph. But even as the empire disintegrated, the civilization that was born within it grew and flourished. Perhaps the most significant sign of a flourishing Islamic civilization was the continued spread of the religion both within and beyond the boundaries of a vanishing Arab Empire (see Map 9.3), although that process differed considerably from place to place. The examples of India, Anatolia, West Africa, and Spain illustrate the various ways that Islam penetrated these societies as well as the rather different outcomes of these epic cultural encounters.