In his research thesis, "Harappa culture and Vedic Literature" Bhagwan Singh has elaborately discussed the conflicts between the then agriculturist and non-agriculturist societies, known as Sur and Asur or Deva and Rakshasa respectively. Sur is from'Su' which denotes activity to produce. Asur is opposite of Sur. Sur and Asur later on became synonym of Deva & Rakshasa respectively. Sur or Deva adopted agriculture for livelihood while Asura or Rakshas were dependent on remaining natural forests. Rakshasa is from the word "Raksha". Asura a Rakshasa were for protection of natural forests while Suras or Devas were cutting, clearing and burning more and more forest areas for extending their agriculture. The practice of sacrificial fires (Havans is reminiscent of this. The infinite numbers of battles mentioned in mythological literature are between these two groups. The Asuras or Rakshasas were not defeated by superior valour, power or armoury of Suras or Devas but because Devas cleared and burnt the natural forests which was the source of food and other supplies for Rakshasas.