Why did the Aryans create the caste system?

It is disputed that the Aryans created the caste system in India. A division of labor is believed to have already existed in India when the Indo-European or lighter-skinned conquerors moved into the area.

The division of labor leading to a caste system included teachers and priests, warriors and rulers, and merchants and peasants. A fifth level of untouchables evolved from those workers dealing in death, pollution or sewage where diseases most likely spread. Keeping society stratified kept the upper class from risk of contamination from these workers. The Aryan association with the upper or warrior class through India's history creates the myth of a superior race.