I don’t think you understand. Take a look at this
And the Indian Empire was dvided into several presidencies for administrative purposes.
If you go before the British, to the Moghul period, during most of that dynasty, the system was the regional and provincial ‘kingdoms’ paid tribute & tax to the emperer in Delhi - in other words the emperor found it administratively convenient to give autonomy to local kinds and nizams but maintain control of the country.
If you go before that you will find the Maurya and a few others that did the same.
If you go even before that, while there is no recorded history in the same level as the above, various legends talk about the entire subcontinent and some lands across the ocean being under the banner, again with local kings paying tribute to a emperor.
This was not unique to India. The Romans did it too