The Constitution grants to Congress the authority to admit new states into the Union. There is a continuing debate over states' rights, which concerns the extent and nature of the states' powers and sovereignty in relation to the federal government and the rights of individuals. The general tendency has been toward centralization and incorporation, with the federal government playing a much larger role than it once did. Over time, the Constitution has been amended, and the interpretation and application of its provisions have changed. Historically, the tasks of local law enforcement, public education, public health, intrastate commerce regulation, and local transportation and infrastructure, in addition to local, state, and federal elections, have generally been considered primarily state responsibilities, although all of these now have significant federal funding and regulation as well. The police power of each state is also recognized.

Additionally, each state has the opportunity to ratify constitutional amendments, and, with the consent of Congress, two or more states may enter into interstate compacts with one another. Each state is also entitled to select a number of electors (equal to the total number of representatives and senators from that state) to vote in the Electoral College, the body that directly elects the president of the United States. States and their citizens are represented in the United States Congress, a bicameral legislature consisting of the Senate and the House of Representatives. territories, possess many powers and rights under the United States Constitution. County or county-equivalent structure varies widely by state, and states also create other local governments.

States are divided into counties or county-equivalents, which may be assigned some local governmental authority but are not sovereign. All are grounded in republican principles (this being required by the federal constitution), and each provides for a government, consisting of three branches, each with separate and independent powers: executive, legislative, and judicial. are allocated power by the people (of each respective state) through their individual state constitutions. State citizenship and residency are flexible, and no government approval is required to move between states, except for persons restricted by certain types of court orders (such as paroled convicts and children of divorced spouses who share child custody). Due to this shared sovereignty, Americans are citizens both of the federal republic and of the state in which they reside. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sovereignty with the federal government. In the United States, a state is a constituent political entity, of which there are 50.

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