They actually don't know for sure what led to the decline but a lot of people believe that the Aryans invaded and conquered the Indus Civilization which would make sense because they were the next people group to live there. I hope this helps!
Answer:
Generally speaking, a key development that occurred globally during the classical era was "D. The expansion of cultural exchange through regional trade", since this was a time of cultural and technological diffusion.
Explanation:
To limit what black people do in the south
