Why do Hindus refer to their religion as Sanatan Dharma?

To start hindu per se is not a religion but its the name given , specifically by the Persians to the inhabitants residing along the banks of the Indus River. Historically all inhabitants of the sub continent were called Hindus. Later its was used to diffrenciate between the the followers of the vedic religion and thse who were not. The term Sanatan Dharna in literal terms means the Eternal Dharma, and Dharma is interpreted to mean the rules or laws that are applied to the Eternal culture or way of living. In addition prefexed to Sanatan Dharma is the word "Satya" meaning truthful. Therefore the religion of India is known as Satya Sanatan Dharma, The enternal way of living based on expounding and living by the principles of Truth, honesty and integrity.