Currently reading: The Rise of Islam and the Bengal Frontier (1204-1760) by Prof. Richard M. Eaton. Absolutely fabulous read from a cultural and historical geography perspective.
As the title implies, it tracks the development of Islam in Bengal from the early Turkish conquest (with the requisite discussion of Buddhist/Hindu religious underpinnings).
Chapter 1 includes a discussion of the ancient Bengal sub-regions without a decent map to show how these coincide with modern boundaries.
So I bring to you gentle readers, a map!
The shaded districts are noted in Eaton's text. I included circles to drive home the idea that the "unshaded" districts are likely part of the same cultural region. So why bother with this?
No less than two cultural sub-regions were split by British partition activities. Varendra (i.e. North Bengal) and Vanga (i.e. Central and southwest Bengal). As Eaton points out in his text, historical development (meaning population, economic, political, cultural) flowed from west to east in Bengal. Thus, the Bhagirathi-Hooghly Basin which could arguably be conceived of the heartland of Bengal is situated wholly within India. Meanwhile, the second heartland (Vanga) got split.
Samatata and Harikela, according to Eaton's text, were initially underdeveloped and hardly "Bengali." Samatata had more in common with the Arakan states and looked to oceanic trade as its actual lifeline.
That continued violence occurs in both Vanga (think Khulna) and Varendra (think Rajshahi) we may hypothesize that the continued split in the cultural region is partly to blame. Though analyzing current events using data from the 13th century is tenuous in some ways, we should pause to reflect. Perhaps this isn't purely coincidental?