What geographic conditions posed the greatest challenge for early civilizations?
(this is about civilizations like the olmec the aztec the incas and indian tribes in north america)
example 1:
example 2:

The civilizations you mention are not that early compared to most. But any civilization needs to have a secure food supply. So a geography that includes an area for good farming would be a necessity. Also, making sure the river you choose to live by is not going to dry up or freeze over every year. I hope that this is the answer that you were looking for and it has helped you.

African americans at the time just came out of slavery and needed money to provide for there families. so they joined for the money mainly.