Historical Map: The Anglo-Irish Treaty, 1921

The Easter Rising of 1916 began a build-up of the Irish nationalist and republican movements which saw Irish public opinion move away from the Irish Parliamentary Party and its aim of Home Rule and towards the idea of an independent Irish Republic, an idea which after 1916 became the goal of the Sinn Féin movement. Founded in 1905, Sinn Féin had originally campaigned for dual monarchy, but just as the Rising and the subsequent execution of its leaders turned the public towards republicanism, so too did it turn Sinn Féin.

Sinn Féin achieved a landslide victory in the 1918 general election, all but destroying the IPP and becoming the largest party in Ireland with 73 seats. The elected members pledged to continue the Irish Republic which had been proclaimed two years before, and in January 1919 they set up their own parliament in Dublin, Dáil Éireann, rather than take their seats in the House of Commons in Westminster. A subsequent election in 1921 saw Sinn Féin hold nearly all of their seats unopposed, though their gains in what was to become Northern Ireland were minimal. The government of the Dáil, led by Éamon de Valera, conducted the War of Independence, which resulted in negotiations between representatives of the Irish and British governments in late 1921. The Irish delegation was led by Arthur Griffith, the founder of Sinn Féin, and Michael Collins, the Minister for Finance in the Dáil.

The eventual result of the negotiations was the Anglo-Irish Treaty. It was far from the independent republic which Sinn Féin had aspired to. An Irish Free State would be created, which would remain within the British Commonwealth. Elected officials would have to swear an Oath of Alleigence to the British monarch before taking their seats in the Dáil, and three Irish ports would remain under British control. The most significant stipulation of the Treaty, however, was that six counties in Ulster would remain within the United Kingdom, in order to assuage the majority Unionist population of those counties.

The Treaty was the subject of much controversy in Ireland. Collins argued that it represented a "stepping stone" in the path to the ultimate goal of an Irish republic, and that the only alternative would be a devastating war with Britain. His opponents argued that it was a capitulation to British demands. The Treaty was debated in Dáil Éireann from December 1921 until January 1922. When voted upon, it was ratified by 64 votes to 57. Upon the ratification, the Anti-Treaty side, led by de Valera, walked out of Dáil Éireann. The divisions which took place in the Dáil quickly spilled out on to the streets, and the soon-to-be Irish Free State was plunged into civil war.

Map detailing how TDs voted on the Treaty. Click to enlarge.
Most of the TDs who voted against the Treaty came from Munster and southern Leinster, while its supporters came from northern Leinster and areas of Connacht and Ulster. Four constituencies in what was to become Northern Ireland were mostly represented by TDs who were representing them alongside their own constituencies: Londonderry by Eoin MacNeill (NUI), Fermanagh and Tyrone by Arthur Griffith and Seán Milroy (both Cavan), Armagh by Michael Collins (Cork Mid, North, South, SE & West) and Down by Éamon de Valera (Clare). Antrim, Dublin University, Queen's University Belfast and the four Belfast City constituencies were not represented in the Dáil as there had been no Sinn Féin TDs elected in those areas. Elected members of the IPP and the Ulster Unionist Party in those regions did not recognise Dáil Éireann.

Pro-Treaty TDs
The number of TDs who voted for the Treaty. Click to enlarge.
* TDs in these constituencies represented them alongside their home constituencies and are only counted once in the total.
The Pro-Treaty TDs would go on to form the Provisional Government of the Irish Free State. With the death of Arthur Griffith and assassination of Michael Collins in August 1923, Carlow-Kilkenny TD W.T. Cosgrave assumed the leadership of the party and of the country. In 1923 they would rename themselves as Cumann na nGaedheal. They remained in government until their defeat in the 1932 general election.

Anti-Treaty TDs
The number of TDs who voted against the Treaty. Click to enlarge.
* TDs in these constituencies represented them alongside their home constituencies and are only counted once in the total.
The Anti-Treaty TDs walked out of Dáil Éireann upon losing the vote. They remained abstentionist after the civil war. In 1926, their leader Éamon de Valera proposed ending abstentionism, but this motion was defeated at a party conference. In response, de Valera and his supporters set up a new party, Fianna Fáil. The new party won 44 seats in the June 1927 general election and entered the Dáil, as it was legally obliged to do under new government legislation. In 1932, Fianna Fáil became the largest party in the Dáil and went into government.