What is the pre-civil war political doctrine that held that the people should decide whether or not to permit slavery?

The doctrine of popular sovereignty was used. That meant that people in those states could choose to vote to support slavery and since they were majority then slavery would be permitted. There were even states that were at first non-slave states but then things changed and they voted to introduce slavery into the state and people voted for this and supported this.

It was butter nut swuash sweetie pie i have no idea