Independent nomadic tribes lived in Saudi Arabia. Then Muhammad unified them giving them a common religion, the Mohammedanism or Islamism.
Muhammad was born in Mecca (570 a. C.). During his youth, he worked in the trade as a caravan driver and he met the Jewish and Christian religions in his travels.
He began to preach the new religion based on the obedience to one God, Allah. The doctrine of Muhammad is contained in the Koran, the holy book of Islam. (See the illustration that a page of the Koran reproduces). Initially, the spread of his ideas was very slow, only his wife Kadixa and some relatives followed him. Muhammad was persecuted and had to flee from the Mecca to Medina. This occurred on 22 September 622, the beginning of the Muslim or Hijri era. From Medina, he started a war and conquered the Mecca, converting the inhabitants to the new religion.