In the last 2500 years, Bengal was under Delhi's or any north Indian based empire's control for just 273 years. Under the Delhi sultanate from 1206-1338 AD and Under the Mughal from 1576-1717 AD. In other times, Bengal was independent kingdom or Sultanate. Ancient Pan-Indian Maurya and Gupta empire were originally started from the north western part of current Bangladesh and West Bengal. Their capital was Patliputra, which is just outside of traditional boundary of historic Bengal. They spoke ancient form of Bangla language. So it can not be claimed that, under Maurya and Gupta empire Bengal was under Indian domination. Actually it is the other way around.Same with Pala empire, Pala expanded their empire from Bengal to other north Indian region.It is only after the Islamic conquest of Indian sub continent when the direction of empire expansion reversed.Still out of 700 years of Muslim rules, Bengal was under Delhi's control for less than 300 years.So, Bengal is in every sense a different realm, separated from North Indian or South Indian geo-political sphere.It's language, culture, outlook are vastly different from North and west Indian based Hindustani culture.Just Because, ancient Bengalis were hindu/buddhist or current West Bengal population are majority hindu does not make Bengalis an Indian people.If that was the parameter then current Bali island hindus or Thai, Cambodian buddhist are also Indian as well despite their entirely different ethnicity, language and culture.