Answer: Wealthy civilizations conquered neighboring areas.
Explanation:
Military conquests have always been an expensive undertaking and this was no different in the ancient world. Wealthier nations were able to field stronger armies as they had the resources to do so.
They would then invade and conquer their neighbours so that they would increase in both power and influence which would enable them gain even more wealth. This is how the empires that controlled the ancient world were born and sustained.
