The founder of Islam was Muhammad in 7th century Arabia. Before Muhammad, Arabia consisted of many polytheistic tribes that fought over resources and trade. Islam is a monotheistic religion based on the Quran, which Muslims believe is the word of God. Muhammad was a merchant from Mecca who received a call from Allah and preached Islam, but moved to Medina in 622 after facing opposition from rich Meccan merchants. This event marks the beginning of the Muslim calendar. Muhammad later conquered Mecca in 628 and spread Islam throughout Arabia.