Sanatana Dharma and Hinduism or Hindu religion is the same thing. In ancient times Persians called the people living on the eastern side of the Indus river as Hindus and named the land on the eastern side of Indus river as Hindustan. The religion which Hindus followed came to be known as Hinduism. Europeans came to know about India in ancient times through Persians so they came to know about Sanatana Dharma from Persian perspective.
