As usual, Wikipedia will give you a general overview of what civilization is.

Before that population densities were lower and people lived basically in hunter gatherer societies and people were generalists- doing everything themselves.

Civilization brought specialization of labor including rulers and warriors. Governments became more formal, caste systems were put into place.

Think about the following:

-the scale of warfare.

-social and economic inequality.

-abuse of power.

– increase in the amount of work for the working classes.

– loss of connection with nature/environmental impact.

– inequality between the sexes.

Flesh those out and consider other areas where complex civilizations have cause problems for people.