Was there ever a genocide that was so successful that a whole culture got wiped out in a short time?

Of course.

The area we know as “North India” today was originally called Madhyadesha - or Middle Nation. For the Bharatas of Ancient and Classical Bharatavarsha, “North” lay quite a bit of distance away, extending from roughly the Vakshu basin to that of the Shatadru centering on what would now be called Swat Valley.

The Bharatas of Madhyadesha branded the Bharatas of Uttarapatha as degenerates, nonetheless it is remarkable just how much the Bharatas of this region contributed to Arya and, by extension, Bharata culture.

The entire land was littered with Cities, Towns, Orchards, Universities, Temples, Gardens, Monasteries. Uttarapatha was where Panini composed his grammars and encyclopedias. Uttarapatha was the route through which passed so much of the Commerce between the East and the West. Uttarapatha is where Kautilya once taught to vast Amphitheatres of students. Uttarapatha is where the Buddha's first disciples walked. Uttarapatha is where the ever-victorious armies of Emperor Ajatashatru ground to a halt and the glittering Eagles and Swastikas of the Gupta Emperors clashed first against the hordes of Asia. Uttarapatha is where, for centuries, stood seven hundred feet tall brick Stupas and hundred feet tall copper statues of Mahadeva. Uttarapatha is where once were built Monoliths whose mere feet once dwarfed Bamiyan five times over. Uttarapatha was where Man first measured the path of Comets and the reckoning of Axial Precession and the nature of Life and Death.

All of it is gone now.

The Monoliths have been, by the labour of centuries of slaves and failing that the might of Artillery, been cast down into dust. The copper statues have been long melted into casings for spears and barrels for guns and wirework for hovels. Where vast cities once stood, now dwell jackals and vermin and fouler creatures. On the banks of pristine lakes where once dwelt ascetics, they've raised prayer halls to their nonexistent demon. In the valleys where once the Vedas were chanted, now sound gunfire and Mleccha gibberish. The Universities are long gone, so are the Palaces and the Gardens and the Observatories and the Temples and the Monasteries, and so goes for Dharma as well- save in Jammu where the educated classes will soon accomplish what a millennium of persecution couldn't.

They've made deserts where once bloomed Mango orchards where visitors from Garyadesha and Romaka once roamed. They've shat on the Buddha's head in once - sacred Monasteries where monks once discussed the reality of Truth. They've raised tribal totems where once Gupta Lords commissioned unequaled artists to paint their murals. And if all that is not enough, I can't even name them lest their pisacha-complexioned Allies, Mlecchas as well, come forth in strength to pen lies against the Past, to mock the Immortal Gods, to silence my feeble words, and sing their uncouth songs of Love and Peace on the ashes of everything.

That is the reality of Kali Yuga. Everything will decline. Everything will shrivel and rot and fade. Everything will end, without even the comfort of oblivion to act as Solace. Everything else is frivolous.