There are limited amounts of resources in a general area. Some civilizations may not have the ability to produce resources that they need. That makes 2 routes:
1) cooperation: They can cooperate with another people group that lives in a different region and trade with them
2) conflict: They can attack/raid another people group in a different region for the resources
hope this helps
Answer:
The longest time period is eons.
Hydrosphere and atmosphere. those are the only 2 spheres that interact with each other in the air.
