Islam began in 610 A.D. when the prophet Muhammad experienced a visit from the angel Gabriel in a cave near Mecca. The Koran, which Muhammad dictated shortly thereafter, is considered to be the word of God through Gabriel's revelations.
When Muhammad returned to Mecca to preach his new religion of a single god, he was persecuted and chased out. He retreated to Medina, where he created an Islamic state and invited other Arabians to follow him. In 630 A.D., after years of fighting and a truce that was violated by the Quraysh, he led his large army into Mecca, which fearfully surrendered without a fight. Most of the citizens converted to Islam.