This is a great thread on Delhi. There is an ecological reason why Delhi becomes the centre of Hindustan from the sultanate period onwards, which Jos Gommans pointed out in a landmark essay, The Silent Frontier of South Asia. https://sci-hub.ee/10.2307/20078711 + https://twitter.com/quizzicalguy/status/1351070630314205189

The argument is that Delhi is on the frontier between the arid zone and the fertile Indo-Gangetic plains. Control of Delhi was key to control mobile communities of the arid zone, who had excellent horses (the region being suited to breeding) as well formed military labour. +

"Delhi was situated very near the rebellious jungles of the Bhattis to the west, which made the position of its rulers rather precarious. In a worst-case scenario, the area could serve not only as a seedbed for rebels but also as a slide for invaders from the northwest" +

"Any invader who managed to gain control of the extensive pastures in Bhatinda and Haryana had a very good chance of controlling Delhi as well. Consequently the Delhi frontier provided the key to political dominion in northern India." +

Well to remember that pre-sultanate 'Hindu' kingdoms in north India were more keen on controlling Kannauj and not Delhi, despite its putative links to the Pandavas. Thus the Bharatiya Vidya Bhavan title, Age of Imperial Kannauj. https://archive.org/details/in.ernet.dli.2015.99501/page/n11/mode/2up /

Ecology and the growing importance of the horse in warfare, thus explain Delhi's rise, than any 'Hindu' past. (end)