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A political union is a type of state which is composed of or created out of smaller states. The process is called unification. Unification of states that used to be together and are reuniting is referred to as reunification. Unlike a personal union or real union, the individual states share a central government and the union is recognized 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 a number of forms, broadly categorized as:
In an incorporating union a new state is created, the former states being entirely dissolved into the new state (albeit that some aspects may be preserved; see below "Preservation of interests").
Incorporating unions have been present throughout much of History such as the Acts of Union, 1707 between the Kingdom of Scotland and the Kingdom of England creating Great Britain, in 1910 the colonies of the Cape of Good Hope, Natal, Orange River Colony, and Transvaal were incorporated into the Union of South Africa, between the years of 1037 to 1479 Spain was in the process of Incorporating the Crown of Castile, Aragon, and Navarre into the Kingdom of Spain, though the process wasn't completed until 1716 (Aragon) and 1833 (Navarre), the Acts of Union 1800 united the Kingdom of Ireland and the Kingdom of Great Britain into the United Kingdom, in 1990 the People's Democratic Republic of Yemen united with Yemen Arab Republic (North Yemen) to form the Republic of Yemen, and in 1783 the Articles of Confederation were signed by each of the Thirteen Colonies, uniting them into the United States of America.
Nevertheless, a full incorporating union may preserve the laws and institutions of the former states, as happened in the creating of the United Kingdom. This may be simply a matter of practice or to comply with a guarantee given in the terms of the union. These guarantees may be to ensure the success of a proposed union, or in the least to prevent continuing resistance, as occurred in the union of Brittany and France in 1532 (Union of Brittany and France), a guarantee was given as to the continuance of laws and of the Estates of Brittany (a guarantee revoked in 1789 at the French Revolution). The assurance that institutions are preserved in a union of states can also occur as states realise that whilst a power imbalance exists (such as between the economic conditions of Scotland and England prior to the Acts of Union 1707), it is not so great that it precludes the ability of concessions to be made. The Treaty of Union for creating the unified Kingdom of Great Britain in 1707 contained a guarantee of the continuance of the civil laws and the existing courts in Scotland (a continuing guarantee), which was significant for both parties. The Scottish, despite economic troubles during the Seven ill years preceding the union, still had remaining negotiating power.
This marks a delineation of states that are able to ensure a preservation of interests, there has to be some mutually beneficial reasoning behind the formal or informal preservation of interests. In the Union creating the United Kingdom of Great Britain and Ireland in 1801, no such guarantee was given for the laws and courts of the Kingdom of Ireland, though they were continued as a matter of practice. The informal recognition of such interests represents the different circumstances of the two Unions, the small base of institutional power in Ireland at the time (those who were the beneficiaries of the Protestant Ascendancy) had faced revolution in the Irish Rebellion of 1798, and as a result there was an institutional drive toward unification, limiting the Irish negotiating power. However, informal guarantees were given to preclude the possibility of further Irish unrest in the period following the French Revolution of 1789 and the 1798 rebellion. These types of informal arrangements are more susceptible to changes, for example Tyrol was guaranteed that its Freischütz companies would not be posted to fight outside Tyrol without their consent, a guarantee later revoked by the Austrian republic. This can be juxtaposed with the continued existence of the Scottish Parliament and a separate body of Scottish Law distinct from English Law.
In an incorporating annexation a state or states is united to and dissolved in an existing state, whose legal existence continues.
Annexation may be voluntary or, more frequently, by conquest.
Incorporating annexations have occurred at various points in history such as in 1535 and 1542 under the two Laws in Wales Acts in which the Kingdom of England formally annexed the Principality of Wales, in 1822 the Republic of Spanish Haiti was annexed by the Republic of Haiti, Prussia/Germany used incorporating annexation to unite many of the German Princes during the Second Schleswig War, the Austro-Prussian War, and the Franco-Prussian War, Sardinia annexed many of the Duchies and City-states in Italy during the period of Italian unification, in 1918 during the Podgorica Assembly the Kingdom of Serbia annexed the Kingdom of Montenegro, and in 1949 and 1951 the People's Republic of China annexed Tibet (1950) and East Turkestan (Xinjiang) (1949).
In a federal or confederal union the states continue in existence but place themselves under a new federal authority. The federal state alone will be the state in international law though the federated states retain an existence in domestic law.
If a unitary state becomes a federated unit of another existing state, the former continuing its legal existence, then that is a federal annexation. The new federated state thus ceases to be a state in international law but retains its legal existence in domestic law, subsidiary to the federal authority.
Federal annexations have occurred in many places, such as British Columbia in 1871, Prince Edward Island in 1873, and Newfoundland in 1949 which were all annexed into Canada, Eritrea was annexed into Ethiopia from 1951 to 1962, Switzerland federally annexed Geneva in 1815, Saarland was federally annexed by West Germany in 1957, Vermont (1791), Texas (1846), and California (1848) all were annexed by the United States of America, and Crimea was annexed into the Russian Federation in 2014.
The unification of Italy involved a mixture of unions. The kingdom consolidated around the Kingdom of Sardinia, with which several states voluntarily united to form the Kingdom of Italy. Others polities, such as the Kingdom of the Two Sicilies and the Papal States, were conquered and annexed. Formally, the union in each territory was sanctioned by a popular referendum where people were formally asked if they agreed to have as their new ruler Vittorio Emanuele II of Sardinia and his legitimate heirs.
The unification of Germany was ultimately a confederal union, but it began in earnest when the Kingdom of Prussia annexed numerous petty states in 1866.
In addition to regional movements, supranational organizations that promote progressive integration between its members started appearing in the second half of the 20th century. Some of these organization were inspired, too some extent by the European Union for example Association of Southeast Asian Nations, the Asia-Pacific Economic Cooperation Forum, and the Pacific Union. Member states are often reluctant to form more centralized unions, the concept of unionism is often present in public debate.
Lord Durham was widely regarded as one of the most important thinkers in the history of the British Empire's constitutional evolution. He articulated clearly the difference between a full legislative union and a federation. In his 1839 Report, in discussing the proposed union of Upper and Lower Canada, he says:
Two kinds of union have been proposed – federal and legislative. By the first, the separate legislature of each province would be preserved in its present form and retain almost all its present attributes of internal legislation, the federal legislature exercising no power save in those matters which may have been expressly ceded to it by the constituent provinces. A legislative union would imply a complete incorporation of the provinces included in it under one legislature, exercising universal and sole legislative authority over all of them in exactly the same manner as the Parliament legislates alone for the whole of the British Isles.