The Anglo-Irish Treaty, officially the ‘Articles of Agreement for a Treaty Between Great Britain and Ireland’, signed on the 6th December 1921, concluded the Irish War of Independence (1919-1921) following the Sinn Féin party’s landslide victory in the 1918 general election in Ireland. The treaty established the Irish Free State as a self-governing dominion within the British Commonwealth of Nations (the Anglo-Irish Treaty contained the UK government’s first use of this term in an official document, rather than the term ‘British Empire’). Ireland was now given complete independence in its domestic affairs: powers to levy all taxes; regulate foreign trade; raise an army; and considerable freedom of foreign policy. The Treaty also provided Northern Ireland, which had been created by the earlier Government of Ireland Act in 1920, with the option to opt out of the Irish Free State; an option that was immediately exercised.

However, the Irish Republican Army (IRA), which saw itself as the legitimate army of the Irish Republic, was deeply split over whether to accept the Treaty. The Treaty caused deep divisions amongst nationalists throughout Ireland, and there were furious debates in the Dáil – the assembly set up by Sinn Féin in 1918. Those who favoured acceptance, such as Michael Collins, the de facto leader of the IRA who had negotiated the Treaty alongside Arthur Griffith, the leader of Sinn Féin, argued that the powers the treaty granted to Ireland made it worthy of support, that it would lead to Irish unity, that it had the support of the majority and was the only alternative to renewed war with Britain. Although Sinn Féin’s ideal settlement would have been the creation of a sovereign, united Irish republic, Griffith had appreciated the British, led by British Prime Minister David Lloyd George, would not accept such terms, and instead aimed to maximise Irish independence and gain a united Ireland. Whilst accepting that it was not end game for the IRA, Collins argued in favour of the treaty on the grounds that it provided Ireland not with ‘the ultimate freedom that all nations desire, but the freedom to achieve it’.
The Treaty’s opponents, on the other hand, criticised it for failing to ‘do the fundamental thing’, that is, to bring about an Irish Republic. The ‘English’ crown would still remain monarch in Ireland, they argued, and government in Ireland would still be conducted in the name of the crown. Whilst conceding that the Treaty had the support of the majority of Irish people, the President of the Republic, Éamon de Valera quipped that: ‘The majority has no right to do wrong.’ de Valera and two of his ministers later resigned in protest. Having declined to take part in the negotiations, de Valera promoted a revision whereby Ireland would have ‘external association’ with the British Commonwealth. Others also noted that Britain also retained its naval bases in Ireland, thereby compromising Irish neutrality in future wars, a particularly thorny issue relating to the belief some still held in the old nationalist adage that ‘England’s extremity is Ireland’s opportunity’.
The Anglo-Irish Treaty was narrowly ratified by Dáil Éireann, the Irish parliament, but conflict was almost inevitable. Membership of the British Empire and the position of the crown were issues upon which Lloyd George could not reasonably have been expected to compromise. However, the same could be said for republican purists, whose political raison d’être was to see an Ireland, fully sovereign, and finally divorced from the British crown. Those within the IRA who rejected these terms rejected not just the Treaty, but also the civilian authorities who had accepted it. This precipitated the outbreak of the Irish Civil War in late June 1922 between pro- and anti-Treaty factions. In June 1922, the first elections were held in the Free State, with Michael Collins’ pro-Treaty Sinn Féin winning a majority of seats. However, violent civil war followed, resulting in an estimated 1,500 deaths with some thousands more injured, leaving the Irish nationalist parties highly polarised and embittered. Another election was held in August 1923, which the pro-Treaty party, now organised as Cumman na nGaedheal, won. The anti-Treatyites finally entered politics as Fianna Fáil in 1927 and came to power peacefully in 1932 – despite widespread rioting between the IRA and the pro-Treaty Blueshirt Movement. By 1939, most of what they considered the objectionable features of the Treaty had been removed by acts of parliament. They and Fine Gael (pro-Treaty) dominated Irish politics for most of the 20th century.