December 7th , 1922
The 1921 Anglo-Irish Treaty, was an agreement between Great Britain and Ireland was signed in London on 6 December 1921, was an agreement between the government of the United Kingdom of Great Britain and Ireland and representatives of the Irish Republic that concluded the Irish War of Independence.
1 Year until Self Governance as Irish Free State
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”.
1 Year to Opt Out of Irish Free State
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 the Parliament of Northern Ireland exercised.
Irish Free State
On the 6th December 1922, a year after the signing of the Anglo-Irish Treaty, the territory of Southern Ireland left the UK and became the Irish Free State, now the Republic of Ireland
Six Counties Opt Out
On the 7th December 1922, The six counties of Northern Ireland opt out of the Free State.
The partition of Ireland was the process by which the Government of the United Kingdom of Great Britain and Ireland divided Ireland into two self-governing polities: Northern Ireland and Southern Ireland.