What geographic conditions posed the greatest challenge for early civilizations? (this is about stuff like mesoamerica, olmec, aztec, and inca, stuff like that)

In that time period civilizations were mostly settling near water indicating fertile soil. All of this should satisfy the needs for food and water in order to survive. Thus, because they were living near water floods represented a great threat, including possible drought.

To have a bunch of countries to team up, and communicate not let the communist break them apart and take over the world