What was the social structure in the new indian civilization? why did reincarnation provide a good reason for this system?

The social structure was based on four castes: the  Brahmins, the Kshatriyas,(land owners) the Vaishas (workers such as merchants) and the Shudas(servants). These castes were hierarchical, that means that the Brahmans had the most power, etc. People would have rebelled against then, but reincarnation gave them hope that in the next life they could have a better caste, so reincarnation has helped to keep the caste system.