Question

in the period before the civil war, the principle of popular sovereignty meant that whether or not a territory allowed slavery would be left up to
a territorial legislatures.
b the united states senate.
c the united states supreme court.
d the president most recently elected.

Explanation:

Popular sovereignty, a key pre-Civil War principle, held that the residents of a territory should decide the slavery issue for themselves. This decision-making power was vested in the elected territorial legislatures, which represented the local population. The other options (Senate, Supreme Court, President) were federal bodies/officials, which went against the core idea of local self-determination in popular sovereignty.

Answer:

A. territorial legislatures.