What were some challenges of Mesopotamia?

Mesopotamian civilization faced many challenges. The first was that the neolithic transition led to increasing urbanization and population density. This meant that areas immediately surrounding cities needed to feed increasing numbers of people while, at the same time, houses and temples were being built on land that might have been used for agriculture. Continuous intensive agriculture eventually depletes and salinizes the soil, meaning that new areas, more distant from the urban center, need to be farmed. To transport food, therefore, one faces the challenge of building transportation networks.
Next, in urban areas, human waste disposal became a problem. Human waste can contaminate drinking water supplies. Also, crowded living conditions can lead to epidemic diseases.
Because the "fertile crescent" was an area rich in arable land and natural resources, nomadic tribes were constantly trying to pillage from the cities and other groups were trying to conquer them.