What historical forces led to the development of complex social groupings in ancient India?

Question

world history

Answer 1

Fierce tribes from the vast plains regions swept down on

India as well as other societies formed for mutual protection.

Attila the Hun and Genghis Kahn at the height of their power

controlled over three quarters of the world. The were virtually unstoppable, even defeating the mighty Roman Legions.

Societies formed to better feed themselves. Tribes had learned the power of numbers in defending against enemies and growing crops and raising domestic animals for food..

they were also able to gain knowledge by the intermingling  of diverse groups who had picked up hunting skills and trade

which was a great advantage.  India was known for its enormous wealth due to tradfing in much sought after spices.