Islam is a monotheistic Abrahamic religion based on the Qur'an. With approximately 1.2-1.3 billion adherents, it is the world's second-largest religion. Followers of Islam are known as Muslims. Muslims believe that God (Alla-h) revealed his word to humanity through many earlier prophets, and that Muhammad was the final prophet. Muslims believe that the core message of Islam, which is submission to God, has been the essential message in the teaching of all God's prophets. The faith went through a period of rapid expansion after Muhammad's death in the 7th century, and its followers can be found all over the world today.
The basic tenet of Islam is found in the shaha-data-n ("two testimonies"): la- ila-ha- illa--lla-hu; muhammadu-r-rasu-lu-lla-hi — "There is no deity other than God (Allah) and Muhammad is the messenger of God (Allah)." A person who truly believes in the meaning of these words is a Muslim. However, for practical reasons one may need to recite the words in the presence of witnesses to be considered one by other members of their faith.
Muslims believe that God (or, in Arabic, Alla-h; also in Aramaic Alaha) revealed his direct word for humanity to Muhammad (c. 570–632) and earlier prophets, including Adam, Noah, Abraham, Moses, and Jesus. Muslims believe that Muhammad is the Last, or the Seal, of the prophets and that his teachings for humanity will last until Qiyamah (The Day of the Resurrection). Muslims assert that the main written record of revelation to humanity is the Qur'an (see below), which they believe to be flawless, immutable, and the final revelation of God to humanity. Muslims believe that parts of the Gospels, Torah and Jewish prophetic books have been forgotten, misinterpreted, incorrectly edited by humans, or distorted by their followers and thus their original message has been corrupted over time (tahrif). With that perspective, Muslims view the Qur'an as a correction of Jewish and Christian scriptures, and a final revelation.
Muslims hold that Islam is essentially the same belief as that of all the messengers sent by God to humanity since Adam, with the Qur'an (the text used by all sects of the Muslim faith) codifying the final revelation of God. Islamic texts depict Judaism and Christianity as derivations of the teachings of Abraham and thus acknowledge common Abrahamic roots. The Qur'an calls Jews and Christians (and sometimes people of other faiths) "People of the Book." Historically, the second Caliph Umar ibn Khattab created what came to be known as "the Pact of Umar" in establishing that any people of the book who submitted to Muslim authority as dhimmis during the wars of Muslim expansion retained their freedom of religion and their existing churches.
Islamic history begins in Arabia in the 7th century with the emergence of Muhammad. Within a century of his death, an Islamic state stretched from the Atlantic ocean in the west to central Asia in the east, which, however, was soon torn by civil wars (fitnas). After this, there would always be rival dynasties claiming the caliphate, or leadership of the Muslim world, and many Islamic states or empires offering only token obedience to an increasingly powerless caliph.
Nonetheless, the later empires of the Abbasid caliphs and the Seljuk Turks were among the largest and most powerful in the world. After the disastrous defeat of the Byzantines at the Battle of Manzikert in 1071, Christian Europe launched a series of Crusades and for a time captured Jerusalem. Saladin, however, restored unity and defeated the Shiite Fatimids.
From the 14th to the 17th centuries, one of the most important Muslim territories was the Mali Empire, whose capital was Timbuktu.
In the 18th century, there were three great Muslim empires: the Ottoman in Turkey, the Middle East, and the Mediterranean; the Safavid in Iran; and the Mogul in India. By the 19th century, these realms had fallen under the sway of European political and economic power. Following WWI, the remnants of the Ottoman empire were parceled out as European protectorates or spheres of influence. Islam and Islamic political power have revived in the 20th century. However, the relationship between the West and the Islamic world remains uneasy.