I didn't know this either. But do are you really comparing some ancient battle to the horror of the Holocaust? Perhaps someone needs a lesson on perspective.
The entire argument that there was any conflict between the Aryans who settled India, and the natives who were pushed into the fringes of the Indian landmass, is controversial.
No record of a violent demise of the Indus Valley Civilisation exists. Not to mention, current evidence points to ecological factors for the destruction of that highly-developed civilisation. No mention of war with natives have been recorded in Hindu scriptures. Most wars detailed are of those between Aryan kingdoms.