A social contract is an agreement between people in a society to cooperate for social benefits, such as giving up their freedoms for protection. So the answer would be "A social contract is based on the belief that people must be willing to give up some of their freedoms to maintain order"
Many Nazi leaders killed themselves before the end of the war because they knew that the war was going to be lost and they did not want to be captured and tortured/killed.
Slaves worked on plantations, where they weren't paid. Thus, this allowed the slave owners to gain money without actually having to physically work on their own plantations.