Vigorous political debate accompanied territorial expansion of the united states before the civil war because a) the texas territory was still under mexican control. b) most people in the united states opposed westward expansion. c) southern states refused to provide the troops necessary for such expansion. d) any new states admitted to the union might upset the sectional balance in congress.

D) any new states admitted to the Union might upset the sectional balance in Congress.

Explanation: Vigorous political debate accompanied territorial expansion of the United States before the Civil War because any new states admitted to the Union might upset the sectional balance in Congress. This "balance" was centered around the number of states that had slavery compared to the number of states that did not allow slavery.

where is the subject? hahahaha