Government of Ireland Act 1920 in the context of "Irish Republic"

Northern Ireland is a part of the United Kingdom in the north-east of the island of Ireland. It has been variously described as a country, province or region. Northern Ireland shares an open border to the south and west with the Republic of Ireland. At the 2021 census, its population was 1,903,175, making up around 3% of the UK's population and 27% of the population on the island of Ireland. The Northern Ireland Assembly, established by the Northern Ireland Act 1998, holds responsibility for a range of devolved policy matters, while other areas are reserved for the UK Government. The government of Northern Ireland cooperates with the government of Ireland in several areas under the terms of the Good Friday Agreement. The Republic of Ireland also has a consultative role on non-devolved governmental matters through the British–Irish Governmental Conference (BIIG).

Northern Ireland was created in 1921, when Ireland was partitioned by the Government of Ireland Act 1920, creating a devolved government for the six northeastern counties. As was intended by unionists and their supporters in Westminster, Northern Ireland had a unionist majority, who wanted to remain in the United Kingdom; they were generally the Protestant descendants of colonists from Britain. Meanwhile, the majority in Southern Ireland (which became the Irish Free State in 1922), and a significant minority in Northern Ireland, were Irish nationalists (generally Catholics) who wanted a united independent Ireland. Today, the former generally see themselves as British and the latter generally see themselves as Irish, while a Northern Irish or Ulster identity is claimed by a significant minority from all backgrounds.

The 1921 Anglo-Irish Treaty (Irish: An Conradh Angla-Éireannach), commonly known in Ireland as The Treaty and officially the Articles of Agreement for a Treaty Between Great Britain and Ireland, was an agreement between the government of the United Kingdom of Great Britain and Ireland and the government of the Irish Republic that concluded the Irish War of Independence. It provided for the establishment of the Irish Free State within a year as a self-governing dominion within the "community of nations known as the British Empire", a status "the same as that of the Dominion of Canada". It also provided Northern Ireland, which had been created by the Government of Ireland Act 1920, an option to opt out of the Irish Free State (Article 12), which was exercised by the Parliament of Northern Ireland.

The agreement was signed in London on 6 December 1921, by representatives of the British government (which included Prime Minister David Lloyd George, who was head of the British delegates, and Winston Churchill, who was Secretary of State for the Colonies) and by representatives of the government of the Irish Republic (which included Michael Collins, who was Secretary of State for Finance, and Arthur Griffith, who was Secretary of State for Foreign Affairs). The Irish representatives had plenipotentiary status (negotiators empowered to sign a treaty without reference back to their superiors) acting on behalf of the Irish Republic, though the British government declined to recognise that status. As required by its terms, the agreement was approved by "a meeting" of the members elected to sit in the House of Commons of Southern Ireland and [separately] by the British Parliament. In reality, Dáil Éireann (the legislative assembly for the de facto Irish Republic) first debated then approved the treaty; members then went ahead with the "meeting". Though the treaty was narrowly approved, the split led to the Irish Civil War, which was won by the pro-treaty side.

The government of Northern Ireland is, generally speaking, whatever political body exercises political authority over Northern Ireland. A number of separate systems of government exist or have existed in Northern Ireland.

Following the partition of Ireland, Northern Ireland was recognised as a separate territory within the authority of the British Crown on 3 May 1921, under the Government of Ireland Act 1920. The new autonomous Northern Ireland was formed from six of the nine counties of Ulster, being four counties with unionist majorities (Antrim, Armagh, Down and Londonderry), and Fermanagh and Tyrone two of the five Ulster counties which had nationalist majorities. In large part unionists, at least in the north east region, supported its creation while nationalists were opposed. Subsequently, on 6 December 1922, the island of Ireland became an independent dominion known as the Irish Free State but Northern Ireland immediately exercised its right to opt out of the new Dominion.

The partition of Ireland (Irish: críochdheighilt na hÉireann) was the process by which the Government of the United Kingdom of Great Britain and Ireland (UK) divided Ireland into two self-governing polities: Northern Ireland and Southern Ireland. It was enacted on 3 May 1921 under the Government of Ireland Act 1920. The Act intended both territories to remain within the United Kingdom and contained provisions for their eventual reunification. The smaller Northern Ireland territory was created with a devolved government (Home Rule) and remained part of the UK. Although the larger Southern Ireland was also created, its administration was not recognised by most of its citizens, who instead recognised the self-declared 32-county Irish Republic.

Ireland had a largely Catholic nationalist majority who wanted self-governance or independence. Prior to partition, the Irish Parliamentary Party used its control of the balance of power in the British Parliament to persuade the government to introduce Home Rule Bills that would give Ireland a devolved government within the UK. This led to the Home Rule Crisis (1912–14), when Ulster unionists founded a large paramilitary organization (at least 100,000 men), the Ulster Volunteers, that could be used to prevent Ulster from being ruled by an Irish government. Although the Government of Ireland Act 1914 (to create a single administration) was passed, implementation was deferred due to the First World War (1914–18). Support for Irish independence grew during the war, particularly in the aftermath of the 1916 Easter Rising (an armed rebellion against British rule).

Northern Ireland is divided into six counties, namely Antrim, Armagh, Down, Fermanagh, Londonderry and Tyrone. Six largely rural administrative counties based on these were among the eight primary local government areas of Northern Ireland from its 1921 creation until 1973. The other two local government areas were the urban county boroughs of Derry (geographically part of the County of Londonderry) and Belfast (geographically split between the counties of Antrim and Down).

The six counties date from the Kingdom of Ireland; five were created between 1570 and 1591 in the Tudor conquest of Ireland, while county Londonderry dates from 1613 and the Plantation of Ulster. The total number of counties in the island of Ireland is 32, with Northern Ireland and the Republic of Ireland often respectively called "the Six Counties" and "the Twenty-Six Counties", especially by Irish nationalists opposed to the partition of Ireland. The 1898–1973 administrative counties were subdivided into county districts. The two-tier county/district system was replaced with a single-tier of "districts", numbering 26 in 1973 and rationalised into 11 in 2015. The areas corresponding to the six counties and two county boroughs remain in use for some administrative purposes, and the six historic counties retain a popular identity.

Southern Ireland (Irish: Deisceart Éireann, pronounced [dʲɛʃcəɾˠt̪ˠ ˈeːɾʲən̪ˠ]) was the larger of the two parts of Ireland that were created when Ireland was partitioned by the Government of Ireland Act 1920. It comprised 26 of the 32 counties of Ireland or about five-sixths of the area of the island, whilst the remaining six counties, which occupied most of Ulster in the north of the island, formed Northern Ireland.

The Act of 1920, which became effective on 3 May 1921, was intended to create two self-governing territories within Ireland, each with its own parliament and governmental institutions, and both remaining within the United Kingdom of Great Britain and Ireland. It also contained provisions for co-operation between the two territories and for the eventual reunification of Ireland. However, in the 1921 elections for Southern Ireland's House of Commons, Sinn Féin candidates won 124 of the 128 seats (all candidates were unopposed and no actual polling occurred), and ignored the parliament, assembling instead as the Second Dáil. The House of Commons of Southern Ireland—consisting of the four unionist members—met only once, while the Senate only met twice. Continuing unrest resulted in the Anglo-Irish Treaty and the Provisional Government, which administered Southern Ireland from 16 January 1922 to 5 December 1922: effectively a transitional administration for the period between the ratifying of the Anglo-Irish Treaty and the establishment of the Irish Free State. Its legitimacy was disputed by the Anti-Treaty delegates to Dáil Éireann.

United Ireland (Irish: Éire Aontaithe), also referred to as Irish reunification or a New Ireland, is the proposition that all of Ireland should be a single sovereign state. At present, the island is divided politically: the sovereign state of Ireland (legally described also as the Republic of Ireland) has jurisdiction over the majority of Ireland, while Northern Ireland, which lies entirely within (but consists of only 6 of 9 counties of) the Irish province of Ulster, is part of the United Kingdom. Achieving a united Ireland is a central tenet of Irish nationalism and Republicanism, particularly of both mainstream and dissident republican political and paramilitary organisations. Unionists support Northern Ireland remaining part of the United Kingdom and oppose Irish unification.

Ireland has been partitioned since May 1921, when the Government of Ireland Act 1920 came into effect, creating two separate jurisdictions—Southern Ireland and Northern Ireland—within the United Kingdom. Southern Ireland never fully functioned and was soon replaced by the Irish Free State in 1922, which became independent, while Northern Ireland opted to remain part of the UK. The Anglo-Irish Treaty, which led to the establishment in December 1922 of a dominion called the Irish Free State, recognised partition, but this was opposed by anti-Treaty republicans. When the anti-Treaty Fianna Fáil party came to power in the 1930s, it adopted a new constitution which claimed sovereignty over the entire island. The Irish Republican Army (IRA) had a united Ireland as its goal during the conflict with British security forces and loyalist paramilitaries from the 1960s to the 1990s known as The Troubles. The Good Friday Agreement signed in 1998, which ended the conflict, acknowledged the legitimacy of the desire for a united Ireland, while declaring that it could be achieved only with the consent of a majority of the people of both jurisdictions on the island, and providing a mechanism for ascertaining this in certain circumstances.

According to the Constitution of Ireland, the names of the Irish state are Ireland (English) and Éire (Irish). From 1922 to 1937, its legal names were the Irish Free State (English) and Saorstát Éireann (Irish). The state has jurisdiction over almost five-sixths of the island of Ireland. The rest of the island is Northern Ireland, a part of the United Kingdom. In 1948 Ireland adopted the terms Republic of Ireland (English) and Poblacht na hÉireann (Irish) as the official descriptions of the state, without changing the constitutional names.

The terms Republic of Ireland (ROI), the Republic, the 26 counties or the South are the alternative names most often encountered. The term "Southern Ireland", although only having legal basis from 1921 to 1922, is still seen occasionally, particularly in Britain.

The Parliament of Northern Ireland was the home rule legislature of Northern Ireland, created under the Government of Ireland Act 1920, which sat from 7 June 1921 to 30 March 1972, when it was suspended because of its inability to restore order during the Troubles, resulting in the introduction of direct rule. It was abolished under the Northern Ireland Constitution Act 1973.

The Parliament of Northern Ireland was bicameral, consisting of a House of Commons with 52 seats, and an indirectly elected Senate with 26 seats. The Sovereign was represented by the governor (initially by the Lord Lieutenant), who granted royal assent to Acts of Parliament in Northern Ireland, but executive power rested with the prime minister, the leader of the largest party in the House of Commons.