Islam originated in Arabia in the seventh century. Founded by the Prophet Muhammad, the religion spread quickly to other parts of Asia, North Africa and Europe and became one of the world's major religions.
Muslims believe that the Prophet Muhammad acted as the messenger of God, or Allah, and that God's revelations to Muhammad have been preserved in the Qur'an. As part of their beliefs, Muslims have a duty to spread their religion, which they did with great effectiveness.
Islam helped to unite the Arabian people, and soon the Arabians spread the religion with their defeat of two of the most powerful empires of the ancient world. The Persian and Byzantine empires had been drained by a conflict with each other, opening them to defeat at the hands of the Muslims.
Arab armies conquered Syria in 636 and conquered the Persian Empire within 10 years of Muhammad's death. The religion also quickly spread into Egypt and North Africa. At its height, Muslim rule stretched from Spain to India.
This quick spread of the Arabian Empire helped to spread the religion of Islam to Egyptians, Persians, Syrians and others. Other factors, such as trade, helped the religion spread further to places like Indonesia, which is home to more Muslims than any other country in the world.