Beneath its legal and creedal unity, the world of Islam harbors a tremendous diversity of cultures, particularly in the outlying regions.

The expansion of Islam can be divided into two broad periods.

In the first period of the Arab conquests, the assimilative activity of the conquering religion was far-reaching.

Although Persia resurrected its own language and a measure of its national culture after the first three centuries of Islam, its culture and language had come under heavy Arab influence.

Only after Safavid rule installed Shi'ism as a distinctive creed in the 16th century did Persia regain a kind of religious autonomy.

The language of religion and thought, however, continued to be Arabic.

In the second period, the spread of Islam was not conducted by the state with 'ulama' influence but was largely the work of Sufi missionaries.

The Sufis, because of their latitudinarianism (tolerant nature), compromised with local customs and beliefs and left a great deal of the pre-Islamic legacy in every region intact.

Thus, among the Central Asian Turks, shamanistic practices were absorbed, while in Africa the holy man and his barakah (an influence supposedly causing material and spiritual well-being) are survivors from the older cults.

In India there are large areas geographically distant from the Muslim religio-political center of power in which customs are still Hindu and even pre-Hindu and in which people worship a motley of saints and deities in common with the Hindus.

The custom of sati, under which a widow burned herself alive along with her dead husband, persisted in India even among some Muslims until late into the Mughal period.

The 18th- and 19th-century reform movements exerted themselves to "purify" Islam of these accretions and superstitions.

Indonesia affords a striking example of this phenomenon.

Because Islam reached there late and soon thereafter came under European colonialism, the Indonesian society has retained its pre-Islamic world view beneath an overlay of Islamic practices.

It keeps its customary law (called adat) at the expense of the Shari'ah; many of its tribes are still matriarchal; and culturally the Hindu epics Ramayana and Mahabharata hold a high position in national life.

Since the 19th century, however, orthodox Islam has gained steadily in strength because of fresh contacts with the Middle East.

Apart from regional diversity, the main internal division within Islamic society is brought about by urban and village life.

Islam originally grew up in the two cities of Mecca and Medina, and as it expanded, its peculiar ethos appears to have developed in urban areas.

Culturally, it came under a heavy Persian influence in Iraq, where the Arabs learned the ways and style of life of their conquered people, who were culturally superior to them.

The custom of veiling women (which originally arose as a sign of aristocracy but later served the purpose of segregating women from men--the pardah), for example, was acquired in Iraq.

Another social trait derived from outside cultures was the disdain for agriculture and manual labor in general.

Because the people of the town of Medina were mainly agriculturists, this disdain could not have been initially present.

In general, Islam came to appropriate a strong feudal ethic from the peoples it conquered.

Furthermore, because the Muslims generally represented the administrative and military aristocracy and because the learned class (the 'ulama') was an essential arm of the state, the higher culture of Islam became urban based.

This city orientation explains and also underlines the traditional cleavage between the orthodox Islam of the 'ulama' and the folk Islam espoused by the Sufi orders of the countryside.

In the modern period, the advent of education and rapid industrialization threatened to make this cleavage still wider.

The westernization of Islam, and the desire to purge Islam of pagan concepts, gave rise to the  strong and widespread fundamentalist movement in the second half of the 20th century, notably among the Taliban, has resulted in widespread religious purging and revolution, especially among the fundamentalists of the Philippines, Indonesia, and Malaysia.