1. Rakshas: A human who has started consuming human meat. To that extent only, they are different from other humans.
2. Devta: Any mineral, solids, gases, liquid, vegetation, living organs in nature including humans are Devta, meaning, THEY EXIST BECAUSE OF ACCEPTED HARMONY; and here Harmony means scientifically accepted proportion of Surs and Asurs. What is accepted harmony will be different for different Devtas. No wonder we have 33 crore(330 million) Devtas.
3. Asurs: Just as we have harmony in nature, we also have disharmony (ASUR) too. Earthquake, storms, hurricanes other natural calamities are perhaps result of not having the right proportion of ratio of harmony and disharmony (ASUR). Obviously increase of Asurs or, using different words, as and when Asurs become powerful Devtas get weaken.