A U.S. state is any one of the fifty subnational entities of the United States that share sovereignty with the federal government (four states use the official title of commonwealth rather than state). Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. However, state citizenship is very flexible, and no government approval is required to move between states (with the exception of convicts on parole).

The United States Constitution allocates power between the two levels of government in general terms. By ratifying the Constitution, each state transfers certain sovereign powers to the federal government. Under the Tenth Amendment, all powers not explicitly transferred are retained by the states and the people. Historically, the tasks of public education, public health, transportation and other infrastructure have been considered primarily state responsibilities, although all have significant federal funding and regulation as well.

Once again, the Constitution has been amended, and the interpretation and application of its provisions have changed. The general tendency has been toward centralization, with the federal government playing a much larger role than it once did. There is a continuing debate over "states' rights", which concerns the extent and nature of the states' powers and sovereignty in relation to that of the federal government, and their power over individuals.

List of states

The following sortable table lists each of the 50 states of the United States with the following information:

1. The common state name
2. The preferred pronunciation of the common state name as transcribed with the International Phonetic Alphabet (see Help:Pronunciation for a key)
3. The United States Postal Service (USPS) two-character state abbreviation
   (also used as the International Organization for Standardization (ISO) Standard 3166-2 country subdivision code)
4. The date the state ratified the United States Constitution or was admitted to the Union
5. The United States Census Bureau estimate of state population as of 2007-07-01
6. The state capital
7. The most populous incorporated place or Census Designated Place within the state as of 2006-07-01, as estimated by the U.S. Census Bureau
8. An image of the official state flag

Union as a single nation

Upon the adoption of the Articles of Confederation and Perpetual Union, the states became a confederation, a single sovereign political entity for the purpose of international law – empowered to levy war and to conduct international relations. In part due to the failings of the Confederation, the thirteen states instead formed a Union via the process of ratifying the United States Constitution, which took effect in 1789.