Popular sovereignty is the principle that the leaders of a state and its government are created and sustained by the consent of its people, who are the source of all political legitimacy. Citizens may unite and offer to delegate a portion of their sovereign powers and duties to those who wish to serve as officers of the state, contingent on the officers agreeing to serve according to the will of the people. In the United States, the term has been used to express this concept in constitutional law. It was also used during the 19th century in reference to a proposed solution to the debate over the expansion of slavery in the United States. The proposal would have given the power to determine the legality of slavery to the inhabitants of the territory seeking statehood, rather than to Congress.