<sigh>
Some days I feel like bursting into tears.
For three years now, I've been saying, to whoever will listen, that on the sub-continent, there are eight river systems around which cultural systems have evolved, and several others isolated around these, which all go into an Indian cultural aggregation. Typically each of these has affiliations to its neighbours, and not any one of them is totally isolated. Just think it over.
The eight rivers around which these cultures have developed are:
The Ganges,
The Brahmaputra,
The Mahanadi,
The Godavari,
The Krishna,
The Kaveri (or Cauvery),
The Narmada,
The Indus.
The others include hill cultures, along the fringes of one or the other of these river systems, the desert culture around the Thar desert, and the forest cultures of central India and north east India.
These cultural building blocks go into more than one independent nation, but do not belong to those nations; in a manner of speaking, the nations belong to them. Pakistan, for instance, almost entirely is defined by what developed around the Indus Valley after the IVC, and the surroundings hills and plains. It is influenced by the desert culture, the Gangetic culture and the Narmada culture, but is distinct from them. They, in turn, are influenced by it, but are distinct from it.
Understanding this makes it clear that ethnicities, languages, cultures, religions are all elements that go into a nation, and it is a grotesque mistake to imagine that the nation goes into the building blocks.
There are thirteen such rivers flowing through Pakistan alone and not five as many believe. The development of river cultures therefore is also distinctly different in many ways. I agree to a large extent of what you have highlighted.
The political India. Of course. In a sense, although strictly speaking, it came into existence in 1857.