Article 4 of the U.S. Constitution defines the relationship of the states toward one another, and their relationship to the federal government. Section 1 contains the "Full Faith and Credit Clause," which requires each state to extend recognition to the public and legal acts of other states.
Section 2 denies criminals the ability to flee to other states to escape justice. If a criminal is apprehended in another state, he is to be returned to the jurisdiction where he was convicted. Section 3 establishes rules for admitting new states into the union. Section 4 is the federal government's guarantee that the states enjoy a republican form of government, and that the federal government defends them from invasion or domestic violence.