The prehistoric Indus Valley civilization is believed to have declined by around 1500BC, and Vedism appeared in its place, with the composition of the Vedas and related Vedic Sanskrit texts.[21] However, it is possible that Vedism was influenced by a substratum of Indus Valley civilization culture......
Actually, the people of this "prehistoric Indus Valley Civilization" also had a religion....which is indeed the VEDIC religion.
AND, HINDUISM is the name given to this very same VEDIC religion..........
You will understand this once you know that the ARYAN invasion of the Indian subcontinent and introduction of the VEDIC religion is a MYTH.....
Myth of The Aryan Invasion and the Harappan Civilization
Death of the Aryan Invasion Theory