Article IV concerns the states.
Section one mandates that all states will honor the laws of all other states. Section 2 guarantees that citizens of one state be treated equally and fairly like all citizens of another. It also says that if a person accused of a crime in one state flees to another, they will be returned to the state they fled from. Section 3 concerns the admittance of new states and the control of federal lands. New states may be admitted to the Union. States cannot be created from parts of other states, nor can two states join together to form one state without the consent of the involved states' legislatures and Congress. Congress has authority over U.S. territories and U.S. property. The Constitution does not in any way give preference to one state over another. Section 4 ensures a republican form of government (which, in this case, is synonymous with "representative democracy," and both of which are opposed to a monarchical or aristocratic scheme - the state derives its power from the people, not from a king or gentry) and guarantees that the federal government will protect the states against invasion and insurrection.