Mecca, according to Muslim tradition, is the city where the Prophet Muhammad received God's message and Islam was born. Over 1,400 years later, the religion has more than 1.5 billion worshipers. But how did it become the fastest-growing religion on Earth? Follow Islam's amazing journey as we explore the cultural heritage of its first converts, nomadic Arab tribes who banded together under this new faith. United, they became a global power that transformed the Middle East, and the world, forever.