Among its main clauses were that:
The contents of the Treaty divided the Irish Republic's leadership, with the President of the Republic, Eamon de Valera, leading the anti-Treaty minority. The main dispute was centred on the Oath of Allegiance, not as is widely claimed, partition; all sides agreed that the Boundary Commission would so reduce Northern Ireland's territory as to make it too small to survive, leading to 'inevitable' Irish unity. (In fact, that did not happen.)
The Second Dáil formally ratified the Treaty in December 1921. (The House of Commons of Southern Ireland, which was made up largely of the same membership as the Dáil, but which was in British constitutional theory the parliament legally empowered to ratify the Treaty, ratafied it in January 1922.) De Valera resigned as President and was replaced by Arthur Griffith. Michael Collins formed a Provisional Government theoretically answerable to the House of Commons of Southern Ireland, as the Treaty laid down. In December 1922 a new Irish constitution was enacted by the Third Dáil, sitting as a Constituent Assembly.
Opponents of the Treaty mounted a military campaign of opposition which produced the Irish Civil War (1922-23). In 1922, its two main Irish signatories, President Griffith and Michael Collins both died. Griffith died partially from exhaustion. Collins, at the signing of the Treaty, said that in signing it, he may have signed his 'actual death warrant'. He was correct. he was assassinated by anti-Treaty republicans in Beal na mBlath in August 1922, barely a week after Griffith's death. Both men were replaced in their posts by W.T. Cosgrave.
The Treaty's provisions relating to the Crown, governor-generalship and its superiority in law were all repealed from the 1922 Constitution by Eamon de Valera, who became President of the Executive Council of the Irish Free State (prime minister) in 1932. Collins argued that the Treaty would give 'the freedom to achieve freedom'. De Valera himself acknowledged the accuracy of this claim both in his actions in the 1930s but also in words he used to describe his opponents and what they did during the 1930s. 'They were magnificent', he told his son in 1932, just after he had entered government and read the files left by Cosgrave's Cumann na nGaedhael Executive Council.
Most people in Ireland today, including members of de Valera's own party, Fianna Fáil agree that it was a mistake to oppose the Treaty and that it was the best deal on offer for the Irish. Britain in 1922 was never going to grant Ireland an independent republic, not least because it could not afford to, without facing similar demands from its dominions. What Ireland got, dominion status on a par of that enjoyed by Canada, New Zealand and Australia, was a massive advance on the forms of Home Rule offered and accepted by Irish leaders like John Dillon, John Redmond and Charles Stewart Parnell.
Furthermore (though it was not generally realised at the time), the IRA was weeks from collapse, with little ammunition or weaponry left. When Collins first heard that the British had called a Truce in mid 1921, following King George V's appeal for reconciliation at the opening of the Northern Ireland, parliament, he commented "we thought they were mad." For the British, though they never realised it, were weeks, perhaps even days away from defeating an exhausted IRA.
De Valera was once asked in a private conversation what had been his biggest mistake. His answer was blunt: "not accepting the Treaty." Current Taoiseach (prime minister and leader of Fianna Fáil) Bertie Ahern has conceded that the date that marks the real achievement of independence is 1922, when the Irish Free State created by the Anglo-Irish Treaty came into being.
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