calling Muslim virus will not explain why if India，as you claimed,  was such a powerful country could be so easily conquered by Muslims, not only them but by all kind of intruders,  "The paramount power of the Great Mogul was broken by the Mogul Viceroys. The power of the Viceroys was broken by the Mahrattas. The power of the Mahrattas was broken by the Afghans, and while all were struggling against all, the Briton rushed in and was enabled to subdue them all.",
The reason is, just as Karl Marx pointed out in 1853, India was "A country not only divided between Mahommedan and Hindoo, but between tribe and tribe, between caste and caste; a society whose framework was base on a sort of equilibrium, resulting from a. general repulsion and constitutional exclusiveness between all its members. Such a country and such a society, were they not the predestined prey of conquest? "
and because of this,  " India, then, could not escape the fate of being conquered, and the whole of her past history, if it be anything, is the history of the successive conquests she has undergone."
"Indian society has no history at all, at least no known history. What we call its history, is but the history of the successive intruders who founded their empires on the passive basis of that unresisting and unchanging society."
so who to blame for this non-history?? Indian themselves.
In particular, as we can see from India's past, ever since Gupta period which is ended in AD 550, India had no hero who could unite the entire Hindustan.
Hinduism will not revival India 's ancient glory,  just as it did not work for the past 1500 yrs for protect India from foreign invasions since Hinduism lacks logic and scientific thinking, but full of superstitious and fantasizing  speculations.