The Muslim world extends continuously from Senegal to Pakistan, and discontinuously eastwards to the Philippines. In 1977 there were some 720 million Muslims, just over a sixth of the world's population. The proportion might have been a great deal higher if the Muslims of Spain had applied themselves more energetically to the conquest of Europe in the eighth century, if the sudden death of Timur in 1405 had not averted a Muslim invasion of China, or if Muslims had played a more prominent role in the modern settlement of the New World and the Antipodes. But they have remained the major religious group in the heart of the Old World. In terms of sheer numbers they are outdone by the Christians, and arguably also by the Marxists. On the other hand, they are considerably less affected by sectarian divisions than either of these rivals: the overwhelming majority of Muslims belong to the Sunni mainstream of Islam.
There are many Muslims at the present day whose ancestors were infidels a thousand years ago; this is true by and large of the Turks, the Indonesians, and sizeable Muslim populations in India and Africa. The processes by which these peoples entered Islam were varied, and reflect a phase of Islamic history when different parts of the Muslim world had gone their separate ways. Yet the core of the Islamic community owes its existence to an earlier and more unitary historical context. Between the seventh and ninth centuries the Middle East and much of North Africa were ruled by the Caliphate, a Muslim state more or less coextensive with the Muslim world of its day. This empire in turn was the product of the . . .