The Ghaznavids were a Persianate Muslim dynasty of Turkic slave origin which existed from 975 to 1187 and ruled much of Persia, Transoxania and some part of present North India.
During the above mentioned period, there were several other great kingdoms exists in the subcontinent. Kings of Kannauj ruled much of the Ganges plain, the Chalukya ruler of the Deccan, the Pala king of Bengal, Pallavas from farther south, Pandyas and the Cholas from still farther south. They all had a considerable size of empire comparable to or even bigger than the empire of Ghaznavids.
But none of those above mentioned kingdoms were able to unite the even half of Indian subcontinend into one kingdom. Even if some of them did it, but not able to hold it for long time. It is the British who has united the present day India , Pakistan and Bangaladesh into one country.