Ethnic assertion is the idea that specific ethnic groups can articulate their own identity in a multilayered and heterogeneous setting. Different texts and thinkers have their own perceptions about the concept and this is especially valid in the case of India. If you have a text or some type of reference point, I would refer to this description before anything else. The concept is unique because it argues that specific groups attempt to reshuffle and advance their own sense of identity in the midst of a diverse element. It's interesting because a sense of nationalism emerges in a cosmopolitan reality. On face value, it seems contradictory, but in nations like India, it's part of the social fabric. In terms of the factors that might be responsible for ethnic assertion, there are many. I would say that religious beliefs or traditional value systems might be a part of this process. I would also suggest that, in some cases, politicians are able to exploit such base assertions in order to solidify or consolidate their own power. The resource below might assist you in being able to continue your exploration of this topic.