What are the political issues caused the most division in washington?

The question is not complete. See below the complete question.

which of these political issues caused the most division in Washington, DC, as the United States moved westward in the 19th century?

A.) the role of men in the new frontier

B.) the role the geography played in state lines

C.) the expansion of slavery into newly acquired territories

D.) whether or not to allow Native Americans to become US citizens

The correct answer is C. The expansion of slavery into newly acquired territories.