Irish Free State in the context of "Revolutions of 1917–1923"

The constitution of the United Kingdom comprises the written and unwritten arrangements that establish the United Kingdom of Great Britain and Northern Ireland as a political body. Unlike in most countries, no official attempt has been made to codify such arrangements into a single document, thus it is known as an uncodified constitution. This enables the constitution to be easily changed as no provisions are formally entrenched.

The Supreme Court of the United Kingdom and its predecessor, the Appellate Committee of the House of Lords, have recognised and affirmed constitutional principles such as parliamentary sovereignty, the rule of law, democracy, and upholding international law. It also recognises that some Acts of Parliament have special constitutional status. These include the Magna Carta, which in 1215 required the King to call a "common counsel" (now called Parliament) to represent the people, to hold courts in a fixed place, to guarantee fair trials, to guarantee free movement of people, to free the church from the state, and to guarantee rights of "common" people to use the land. After the Glorious Revolution, the Bill of Rights 1689 and the Claim of Right Act 1689 cemented Parliament's position as the supreme law-making body, and said that the "election of members of Parliament ought to be free". The Treaty of Union in 1706 and the Acts of Union 1707 united the Kingdoms of England, Wales and Scotland, the Acts of Union 1800 joined Ireland, but the Irish Free State separated after the Anglo-Irish Treaty in 1922, leaving Northern Ireland within the UK. After struggles for universal suffrage, the UK guaranteed every adult citizen over 21 years the equal right to vote in the Representation of the People (Equal Franchise) Act 1928. After World War II, the UK became a founding member of the Council of Europe to uphold human rights, and the United Nations to guarantee international peace and security. The UK was a member of the European Union, joining its predecessor in 1973, but left in 2020. The UK is also a founding member of the International Labour Organization and the World Trade Organization to participate in regulating the global economy.

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 United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland, with a population of over 69 million in 2024. The UK includes the island of Great Britain, the north-eastern part of the island of Ireland, and most of the smaller islands within the British Isles, covering 94,354 square miles (244,376 km). It shares a land border with the Republic of Ireland and is otherwise surrounded by the Atlantic Ocean, the North Sea, the English Channel, the Celtic Sea and the Irish Sea, while maintaining sovereignty over the British Overseas Territories. The capital and largest city of both England and the UK is London; Edinburgh, Cardiff and Belfast are the national capitals of Scotland, Wales and Northern Ireland.

Britain has been inhabited since the Neolithic. In AD 43 the Roman conquest of Britain began. The Roman departure between 383 and 410 was followed by Anglo-Saxon settlement beginning around 450. In 1066 the Normans conquered England. After the Wars of the Roses, the Kingdom of England began to flourish, resulting in the 16th-century annexation of Wales and the establishment of the British Empire. Over the 17th century the role of the British monarchy was reduced, particularly as a result of the English Civil War. In 1707 the Kingdom of England and the Kingdom of Scotland united under the Treaty of Union to create the Kingdom of Great Britain. In the Georgian era the office of prime minister became established. The Acts of Union 1800 incorporated the Kingdom of Ireland to create the United Kingdom of Great Britain and Ireland in 1801. Most of Ireland seceded from the UK in 1922 as the Irish Free State, and the Royal and Parliamentary Titles Act 1927 created the present United Kingdom.

Ireland (Irish: Éire [ˈeːɾʲə] ), also known as the Republic of Ireland (Poblacht na hÉireann), is a country in Northwestern Europe. It consists of 26 of the 32 counties of the island of Ireland, with a population of about 5.4 million. Its capital and largest city is Dublin, on the eastern side of the island, with a population of over 1.5 million. The sovereign state shares its only land border with Northern Ireland, which is part of the United Kingdom. It is otherwise surrounded by the Atlantic Ocean, with the Celtic Sea to the south, St George's Channel to the south-east and the Irish Sea to the east. It is a unitary, parliamentary republic. The legislature, the Oireachtas, consists of a lower house, Dáil Éireann; an upper house, Seanad Éireann; and an elected president (Uachtarán) who serves as the largely ceremonial head of state, but with some important powers and duties. The head of government is the Taoiseach (prime minister, lit. 'chief'), elected by the Dáil and appointed by the president, who appoints other government ministers.

The Irish Free State was created with Dominion status in 1922, following the Anglo-Irish Treaty. In 1937, a new constitution was adopted, in which the state was named "Ireland" and effectively became a republic, with an elected non-executive president. It was officially declared a republic in 1949, following The Republic of Ireland Act 1948. Ireland became a member of the United Nations in 1955. It joined the European Communities (EC), the predecessor of the European Union (EU), in 1973. The state had no formal relations with Northern Ireland for most of the 20th century, but the 1980s and 1990s saw the British and Irish governments working with Northern Irish parties to resolve the conflict that had become known as the Troubles. Since the signing of the Good Friday Agreement in 1998, the Irish government and Northern Irish government have co-operated on a number of policy areas under the North/South Ministerial Council created by the Agreement.

A dominion was any one of several largely self-governing countries that remained, especially in the first half of the 20th century, under the British Crown as parts of the British Empire and then the British Commonwealth of Nations. The list of dominions as at 1926 included Australia, Canada, the Irish Free State, New Zealand, Newfoundland, and South Africa; later Ceylon (now Sri Lanka), India, and Pakistan also became dominions for short periods. Progressing from colonies, their degrees of colonial self-governance increased (and, in one case, decreased) but did so unevenly over the late 19th century through the 1930s. In the years following the Second World War, the British Empire was refashioned into the more modern (and more post-colonial) Commonwealth of Nations (after which the former dominions were often referred to as the Old Commonwealth). By the time this transition was formally finalised, in 1949, the old dominions had become more autonomous and independent nation states, each in their own right, either as a Commonwealth republic or a Commonwealth realm.

In 1925, the government of the United Kingdom created the Dominions Office from the Colonial Office, although for the next five years they shared the same secretary in charge of both offices. "Dominion status" was first accorded to Australia, Canada, the Irish Free State, New Zealand, Newfoundland, and South Africa at the 1926 Imperial Conference through the Balfour Declaration of 1926, recognising Great Britain and the Dominions as "autonomous communities within the British Empire, equal in status, in no way subordinate one to another in any aspect of their domestic or external affairs, though united by a common allegiance to the Crown and freely associated as members of the British Commonwealth of Nations". Their full legislative independence was subsequently confirmed in the Statute of Westminster 1931. In the 1920s and 1930s, they began to represent themselves in international bodies, in treaty making, and in foreign capitals. Vestiges of empire and colonial rule lasted in some dominions late into the 20th century and indeed still exist today.

The House of Commons is the lower house of the Parliament of the United Kingdom. Like the upper house, the House of Lords, it meets in the Palace of Westminster in London, England. The House of Commons is an elected body consisting of 650 members known as members of Parliament (MPs), who are elected to represent constituencies by the first-past-the-post system and hold their seats until Parliament is dissolved.

The House of Commons of England began to evolve in the 13th and 14th centuries. In 1707 it became the House of Commons of Great Britain after the political union with Scotland, and from 1801 it also became the House of Commons for Ireland after the political union of Great Britain and Ireland. In 1922, the body became the House of Commons of the United Kingdom of Great Britain and Northern Ireland after the independence of the Irish Free State. Under the Parliament Acts 1911 and 1949, the Lords' power to reject legislation was reduced to a delaying power. The government is solely responsible to the House of Commons and the prime minister stays in office only as long as they retain the confidence of a majority of the Commons.

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 United Kingdom of Great Britain and Ireland was the union of the Kingdom of Great Britain and the Kingdom of Ireland into one sovereign state, established by the Acts of Union in 1801. It continued in this form until 1927, when it evolved into the United Kingdom of Great Britain and Northern Ireland, after the Irish Free State gained a degree of independence in 1922.

Rapid industrialisation that began in the decades prior to the state's formation continued up until the mid-19th century. The Great Irish Famine, exacerbated by government inaction in the mid-19th century, led to demographic collapse in much of Ireland and increased calls for Irish land reform. The 19th century was an era of Industrial Revolution, and growth of trade and finance, in which Britain largely dominated the world economy. Outward migration was heavy to the principal British overseas possessions and to the United States.