Hindus believe in the repetitious Transmigration of the Soul . This is the transfer of one's soul after death into another body. This produces a continuing cycle of birth, life, death and rebirth through their many lifetimes. It is called samsara . Karma is the accumulated sum of ones good and bad deeds. Karma determines how you will live your next life. Through pure acts, thoughts and devotion, one can be reborn at a higher level. Eventually, one can escape samsara and achieve enlightenment. Bad deeds can cause a person to be reborn as a lower level, or even as an animal. The unequal distribution of wealth, prestige, health, disability, suffering, etc. are thus seen as natural consequences for one's previous acts, both in this life and in previous lives.
For many centuries the caste system worked in a super manner, creating and consolidating the Indian culture, which reached its height when the Brahmins, Kshatriyas, Vaisyas, and Sudras all dedicated their activities and efforts to the common welfare. But in this relative universe even a good custom, if it continues for a long time, becomes corrupted. The Brahmins had a monopoly of the knowledge of the scriptures, which was the source of their power; eventually they became greedy for more and began to exploit the lower castes. They demanded privileges and respect even when they did not possess Brahminical qualities. Similarly, the Kshatriyas and the Vaisyas exploited the Sudras, who formed the majority of the population. The social laws became rigid, and in the absence of freedom Hindu society stagnated. On account of exploitation, the masses became weak and the country fell an easy prey to powerful invaders from the outside. Islam and Christianity took advantage of the injustices that prevailed in Hindu society and made easy converts, especially among those who were denied social privileges. Hindu society, however, was not completely to blame; for these foreign religions also sometimes used force and unethical persuasion for the purpose of conversion.