How did the geography of the Indian subcontinent influence the development of civilization there?

The most important element of Indian civilization to
influence development of civilization was the sub-continent's river system.  The
earliest civilization, the Dravidian, developed along the Indus River which, like the
Nile in Africa, flooded and deposited rich soil carried from upstream which made
agriculture possible. Unlike the Nile which was somewhat predictable, the flooding of
the Indus was arbitrary and capricious. 'The Harapan society occupied all of present day
Pakistan and much of Northern India. Its people were the first to domesticate chickens,
and also grew large amounts of cotton, wheat and
barley.

There is evidence the Dravidian civilization went
into decline because of deforestation as more land was cleared for planting.
Unfortunately, their language has not yet been deciphered and must of the remains of
their largest cities are underwater; so there is little known about their culture or
religion.