Geography of Ancient India - The Indus River Valley

The culture that developed in the Indus River Valley around 3500-2500 BC, referred to by some as the Harappan Culture (named for Harappa, one of the ruined cities of the ancient civilization), was cut off from others on all sides by its geography.

The Chinese cultures were to the north and northeast, past the giant Himalayas. Crossing the Thar Desert and thick jungles to the east, one would have come to the early people of the Ganges River Valley. The Indus people were isolated from the Mesopotamians and other near-east cultures to the west / northwest by the Hindu Kush and vast deserts. Finally, the people of the Indus Valley were hemmed in to the south by the Arabian Sea / Indian Ocean. Nevertheless, the Indus River civilization flourished and grew to control more land (on the order of 500,000 square miles) than either the ancient Egyptians or the Mesopotamians.
Even though it developed interdependently from the other river valley civilizations, the success of the Indus Valley Civilization was due in large part to the Indus River itself. Fed by monsoonal summer rains and winter runoff from the mountains, the Indus River, especially when seen from space, is an obvious oasis in an otherwise bleak looking region.
To the Indus Valley people, the river provided fertile grounds to crops of rice, wheat, various fruits and vegetables, and cotton. In addition, the Indus provided grazing lands for herd animals and, of course, a steady supply of fresh water.
Ironically, the Indus and the geography of the region provide for speculation about the mysterious end of the Indus Valley civilization. Some theorize that earthquakes and abnormally large and frequent floods caused the end for the Indus people. One theory even suggests that the Indus River itself changed course, thereby forcing the people to leave.
Resources: Wikipedia (Indus River) (Indus Valley Civilization)