Article 4, Section 4

The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

The federal government ensures that each state must maintain a representative form of government; no state is allowed to become a dictatorship. The federal government also promises to protect all the states from foreign military attack, and to come to the aid of the states if they are threatened by uprisings or insurrections.