Reserved powers in the context of "Everything which is not forbidden is allowed"

A political union is a type of political entity which is composed of, or created from, smaller polities or the process which achieves this. These smaller polities are usually called federated states and federal territories in a federal government; they are called prefectures, regions, or provinces in the case of a centralised government. This form of government may be created through voluntary and mutual cession and is described as unionism by its constituent members and proponents. In other cases, it may arise from political unification, characterised by coercion and conquest. The unification of separate states which, in the past, had together constituted a single entity is known as reunification. Unlike a personal union or real union, the individual constituent entities may have devolution of powers but are subordinate to a central government or coordinated in some sort of organization. In a federalised system, the constituent entities usually have internal autonomy, for example in the setup of police departments, and share power with the federal government, for whom external sovereignty, military forces, and foreign affairs are usually reserved. The union is recognised internationally as a single political entity. A political union may also be called a legislative union or state union.A union may be effected in many forms, broadly categorized as:

• Incorporating union
• Incorporating annexation
• Federal union
• Federative annexation
• Mixed unions

In American political discourse, states' rights are political powers held for the state governments rather than the federal government according to the United States Constitution, reflecting especially the enumerated powers of Congress and the Tenth Amendment. The enumerated powers that are listed in the Constitution include exclusive federal powers, as well as concurrent powers that are shared with the states, and all of those powers are contrasted with the reserved powers—also called states' rights—that only the states possess. Since the 1940s, the term "states' rights" has often been considered a loaded term, a euphemism, or a dog whistle because of its use in opposition to federally-mandated racial desegregation and, more recently, same-sex marriage and reproductive rights.

The Tenth Amendment (Amendment X) to the United States Constitution, a part of the Bill of Rights, was ratified on December 15, 1791. It expresses the principle of federalism, whereby the federal government and the individual states share power, by mutual agreement. The Tenth Amendment prescribes that the federal government has only those powers delegated to it by the Constitution, and that all other powers not forbidden to the states by the Constitution are reserved to each state, or to the people.

The amendment, with origins before the American Revolution, was proposed by the 1st United States Congress in 1789 during its first term following the adoption of the Constitution. It was considered by many members as a prerequisite before they would ratify the Constitution, and particularly to satisfy demands of Anti-Federalists, who opposed the creation of a stronger federal government.

Concurrent powers are powers of a federal state that are shared by both the federal government and each constituent political unit, such as a state or province. These powers may be exercised simultaneously within the same territory, in relation to the same body of citizens, and regarding the same subject-matter. Concurrent powers are contrasted with reserved powers (not possessed by the federal government) and with exclusive federal powers (forbidden to be possessed by the states, or requiring federal permission).

In many federations, enumerated federal powers are supreme and so, they may pre-empt a state or provincial law in case of conflict. Concurrent powers can therefore be divided into two kinds: those not generally subject to federal pre-emption, such as the power to tax private citizens, and other concurrent powers.