Complex sentence: Dixon Line symbolizes a cultural boundary between the Northeastern United States and the Southern United States (Dixie) and legality of slavery as a result, although the Missouri Compromise Line had much more definitive geographic connection to in the United States leading up to the Civil War.
Split into simpler sentences: Dixon Line symbolizes a cultural boundary between the Northeastern United States and the Southern United States (Dixie) and legality of slavery as a result. Though the Missouri Compromise Line had much more definitive geographic connection to in the United States leading up to the Civil War.