According the University of Texas, the U.S. Constitution prohibits the states from entering into treaties, alliances, or confederations, coining money, emitting bills of credit, paying debts in anything but gold and silver coin, taxing imports or exports and entering into an agreement or compact with another state or foreign government. The U.S. Constitution also governs certain aspects of state relations and denies Congress certain powers.
The University of Texas notes that the U.S. Constitution requires states grant full faith and credit to public acts, records and judicial proceedings. It also requires that states respect all of the privileges and immunities that U.S. citizens enjoy. States must allow for the extradition of fugitives. The Constitution also provides rules for the admission of new states to the Union and guarantees that the national government protects states from foreign invaders.
According to the University of Texas, the 10th Amendment of the U.S. Constitution reserves all powers to the states that are not delegated to the United States or prohibited by the Constitution. This is known as the reserved powers clause. The Constitution also limits the powers of Congress. Congress cannot suspend privilege of habeas corpus, impose taxes on exports from the states or grant titles of nobility.