How did people make the land habitable in ancient India?

Ancient Indian civilization dates back to around 3300 BC. This civilization was called Harappan, its main habitat was the valley of the Indus River. So the ancient Hindus were engaged in agriculture (gathering, farming and cattle breeding). True, a significant part of the territory of India was covered with jungle, which made it impossible for people to expand agriculture, but over time, people learned how to clear them and made them suitable for habitation. So at one time the valley of the Ganges River, where once upon a time there was an impenetrable jungle, became suitable for habitation.