I recently added Caste by Isabel Wilkerson to the Recommended Reading List.

Wilkerson explores inequity via social hierarchy primarily in the United States and India.  In the case of India the caste system is the primary tool; in America it is race.

She contends that any such system requires a bottom caste in order to thrive and that people marginally in an upper caste – like poor, less skilled and educated whites in America –  will cling to their supposed superior caste membership even at the price of their self-interest.