Answer :
Ancient history of India is intertwined with the River 'sindhu' (Indus) that gave the people & country the name (Hindu & Hindustan - India). Ganga (Ganges) flowing in the middle of Northern Indian plains came much later into the picture. People coming from the highlands & plateau of Central Asia as also the Greeks form Macedonia, as soon as they descend from the high dry mountain passes, they first see the plains of Indus & its tributaries draining a vast territory (Indus is 20th longest & 21 largest in area drained). This view form the mountains to the plains below was endured by hordes from Central Asia for the last 4000 years at least. All of them hardy, uncouth fighters who had to lead a hard life succumbed to the easy charms & luxury of the country in well watered plains and remained, becoming civilized and started fighting newer waves of marauders pouring through the same passes. So it went on, through out history till the European Empire builders made entry from the opposite end, from the sea. It changed Indians' orientation (or did it really !) of how they looked at their country. Pakistan lays along the course of Indus, and is said to be the 'Modern day Indus valley'. All ancient scriptures & legends are full of references to places there & even the places' names (Multan, Taxila. Peshawar) are redolent with this ancient, pre-Islamic folklore.