Romila Thapar notes that the division into Hindu-Muslim-British periods of Indian history gives too much weight to "ruling dynasties and foreign invasions", neglecting the social-economic history which often showed a strong continuity. The division into Ancient-Medieval-Modern periods overlooks the fact that the Muslim conquests occurred gradually during which time many things came and went off, while the south was never completely conquered. According to Thapar, a periodisation could also be based on "significant social and economic changes", which are not strictly related to a change of ruling powers.[note 1]