The main reason why Congress worked to keep a balance between the number of slaveholding states and free states is because they wanted to avoid war breaking out between the North and the South. They tried to do this through a series of compromises that ultimately failed.
Historians have identified the basic characteristics of civilizations. Six of the most important characteristics are: cities, government, religion, social structure, writing and art.
That is difficult, I'm not exactly sure what the context is but... I would answer with the Nile River
