The Muslim conquest of the Indian subcontinent led to widespread carnage because Muslims regarded the Hindus as infidels and therefore slaughtered and converted millions of Hindus.
Will Durant argued in his 1935 book "The Story of Civilization: Our Oriental Heritage" (page 459):
The Mohammedan conquest of India is probably the bloodiest story in history. The Islamic historians and scholars have recorded with great glee and pride the slaughters of Hindus, forced conversions, abduction of Hindu women and children to slave markets and the destruction of temples carried out by the warriors of Islam during 800 AD to 1700 AD. Millions of Hindus were converted to Islam by sword during this period.
