m from French civil law.
Only a few states choose to have the judges on the state's courts serve for life terms. In most of the states the judges, including the justices of the highest court in the state, are either elected or appointed for terms of a limited number of years, such as five years, eligible for re-election or reappointment if their performance is judged to be satisfactory.
Under Article Four of the United States Constitution, which outlines the relationship between the states, the United States Congress has the power to admit new states to the Union. The states are required to give full faith and credit to the acts of each other's legislatures and courts, which is generally held to include the recognition of legal contracts and criminal judgments, and before 1865, slavery status. Regardless of the Full Faith and Credit Clause, some legal arrangements, such as professional licensure and marriages (e.g. same-sex marriages), may be state-specific, and states have not been found by the courts to be required to honor such arrangements from other states.11
Such legal acts are nevertheless often recognized state-to-state according to the common practice of comity. States are prohibited from discriminating against citizens of other states with respect to their basic rights, under the Privileges and Immunities Clause. Under the Extradition Clause, a state must extradite people located there who have fled charges of "treason, felony, or other crimes" in another state if the other state so demands. The principle of hot pursuit of a presumed felon and arrest by the law officers of one state in another state are often permitted by a state.12
With the consent of Congress, states may enter into interstate compacts, agreements between two or more states. Compacts are frequently used to manage a shared resource, such as transportation infrastructure or water rights.13
Four states use the official name of Commonwealth, rather than State.14 However, this is merely a paper distinction, and the U.S. Constitution uniformly refers to all of these subnational jurisdictions as "States" (Article One, Section 2, Clause 1 of the Constitution, concerning the U.S. House of Representatives, in which Representatives are to be elected by the people of the "States"; Article One, Section 3, Clause 1, concerning the U.S. Senate, allocates to each "State" two Senators). For all of these purposes, each of the four above-mentioned "Commonwealths" counts as a State.
Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50. The U.S. Constitution is rather laconic on the process by which new states could be added, noting only that "New States may be admitted by the Congress into this Union" and forbidding a new state to be created out of the territory of an existing state, or the merging of two or more states into one, without the consent of both Congress and all the state legislatures involved.
In practice, most of the states admitted to the union after the original 13 have been formed from Territories of the United States (that is, land under the sovereignty of the federal government but not part of any state) that were organized (given a measure of self-rule by the Congress subject to the Congress’ plenary powers under the territorial clause of Article IV, sec. 3, of the U.S. Constitution).15
Generally speaking, the organized government of a territory made known the sentiment of its population in favor of statehood, usually by referendums. Congress then directed that government to organize a constitutional convention to write a state constitution. Upon acceptance of that Constitution, Congress has always admitted that territory as a state. The broad outlines in this process were established by the Northwest Ordinance (1787), which predated the ratification of the Constitution.
However, Congress has ultimate authority over the admission of new states, and is not bound to follow this procedure. A few U.S. states (outside of the original 13) that were never organized territories of the feder