Southern Ireland (1921–22) in the context of "Second Dáil"

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).

The Parliament of Southern Ireland was a Home Rule legislature established by the British Government during the Irish War of Independence under the Government of Ireland Act 1920. It was designed to legislate for Southern Ireland, a political entity which was created by the British Government to solve the issue of rising Irish nationalism and the issue of partitionism, while retaining the whole of Ireland as part of the United Kingdom.

The parliament was bicameral, consisting of a House of Commons (the lower house) with 128 seats and a Senate (the upper house) with 64 seats. The parliament as two houses sat only once, in the Royal College of Science for Ireland in Merrion Street. Due to the low turnout of members attending, the parliament was adjourned sine die and was later officially disbanded by the Irish Free State (Agreement) Act 1922.

In international relations, a partition is a division of a previously unified territory into two or more parts.

Brendan O'Leary distinguishes partition, a change of political borders cutting through at least one territory considered a homeland by some community, from secession, which takes place within existing recognized political units. For Arie Dubnov and Laura Robson, partition is the physical division of territory along ethno-religious lines into separate nation-states.

The Ulster Volunteers was an Irish unionist, loyalist paramilitary organisation founded in 1912 to block domestic self-government ("Home Rule") for Ireland, which was then part of the United Kingdom. The Ulster Volunteers were based in the northern province of Ulster. Many Ulster Protestants and Irish unionists feared being governed by a nationalist Catholic-majority parliament in Dublin and losing their links with Great Britain. In 1913, the militias were organised into the Ulster Volunteer Force (UVF) and vowed to resist any attempts by the British Government to impose Home Rule on Ulster. Later that year, Irish nationalists formed a rival militia, the Irish Volunteers, to safeguard Home Rule. In April 1914, the UVF smuggled 25,000 rifles into Ulster from Imperial Germany. The Home Rule Crisis was interrupted by the First World War. Much of the UVF enlisted with the British Army's 36th (Ulster) Division and went to fight on the Western Front.

After the war, the British Government decided to partition Ireland into two self-governing regions: Northern Ireland (which overall had a Protestant/unionist majority) and Southern Ireland. However, by 1920 the Irish War of Independence was raging and the Irish Republican Army (IRA) was launching attacks on British forces in Ireland. In response, the UVF was revived. It was involved in some sectarian clashes and minor actions against the IRA. However, this revival was largely unsuccessful and the UVF was absorbed into the Ulster Special Constabulary (USC), the new reserve police force of Northern Ireland.