Romila Thapar notes that the division of 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 in Ancient-Medieval-Modern overlooks the fact that the Muslim-conquests took place between the eight and the fourteenth century, 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.