I am writing an essay about the civil war. Are "the south" and "the north" proper nouns or common nouns?

Confederacy and Union are more accurate and scholarly titles.

If you are using them to identify a group of people, or a political movement, etc., then they are proper nouns. If you are using them only to indicate direction, "the army moved north", then they are common.

proper in that connotation

Royalists and Parliamentarians would be more appropriate. The Civil War was not divided on North/South lines so it is meaningless to use those terms.