The Concise Oxford Dictionary of World Religions (1107 page)

ammad died, no exact provision had been made for any successor to lead the new community. Those who looked for the most effective leader chose Abu Bakr, known as caliph or
khal
fa
. Those who looked for the closest relative of Mu
ammad supported
‘Al
. Although there were four immediate successors (al-R
shid
n; see
KHAL
FA
) before a final split, the strains were too great, and the party (
sh
‘a
) of ‘Al
broke away from those who claimed to be following the custom (
sunna
) of the Prophet, thereby creating the divide between Sunni and
Sh
‘a
Muslims which persists to this day.
The spread of Islam was extremely rapid. Within a hundred years of the death of Mu
ammad, it had reached the Atlantic in one direction and the borders of China in the other. It now amounts to about a billion adherents, and is found in most countries of the world. At one stage (from the 9th to the 13th cents. CE), the Muslim delight in creation led it into a passionate commitment to
knowledge
(
‘ilm
), which in turn led Muslims into spectacular achievements in philosophy (
falsafa
) and the natural sciences.
There were two major reactions to the achievements of Muslim philosophy and science. The first was a growing suspicion that perhaps the achievements of the human mind were taking priority over the revelation from God. ‘The Incoherence of Philosophy’ was exposed by
al-Ghaz(z)
l
(1058–1111 (AH 450–505)), and since that time the prevailing tendency has been one of giving priority to revelation (and the sciences associated with it of exegesis) and obedience.
The second major reaction was a reinforcement of that style of Muslim life and devotion which is known as
Sufism
.
Islam is necessarily a
missionary
religion, since entrusted to it is the revelation of God's word and will for the world. The world is divided into three domains (see
D
R AL-HARB