It is difficult to generalize about Islam. To begin with, the word itself is commonly used with two related but distinct meanings, as the equivalents both of Christianity, and Christendom. In the one sense, it denotes a religion, as system of beliefs and worship; in the other, the civilization that grew up and flourished under the aegis of that religion. The word Islam thus denotes more than fourteen centuries of history, a billion and a third people, and a religious and cultural tradition of enormous diversity.