A major cause of the Protestant Reformation was the sale of indulgences by the Catholic Church. Martin Luther began early in his writings criticizing this practice in saying that the Pope had no authority or right to sell this type of indulgence.
The correct answer is inferior courts.
The US Constitution gives Congress the ability to create inferior courts as a means to provide federal rulings on issues between different states without having to go through the Supreme Court. Considering the size of the nation, lower federal courts are needed in order to effectively addresss all of the legal problems within the United States. Just having the Supreme Court would be extremely ineffective, as they can only hear so many cases in a year.
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.
