Popular sovereignty refers to a principle developed in the Enlightenment period. This concept is particularly associated with philosophers such as Hobbes, Locke and Rousseau. The principle states that government exists only because of the consent of people, but that the political power of the nation lies on the people, and not on government. This is shown in the way that the people of the United States are represented in Congress. People are able to vote for their leaders and expect them to represent their interests because the ultimate political authority lies with the people.
On the other hand, republicanism refers to a form of government organization in which people are considered citizens and are allowed to participate in government. Republicanism is closely connected with liberalism. This is shown in the way Congress operates because Congressmen are meant to represent the citizens. Citizenship of a nation-state is what gives people the ability to vote for representatives, the opportunity to participate in government and the individual right to decide the future of the country.