By the end of the 1910s, Ulster’s exclusion from the Home Rule Act was almost inevitable, but the precise form this would take was still to be decided. In late 1919, the British Government formed a committee headed by Irish unionist Walter Long to determine Ulster’s fate.
The Government of Ireland Act
The ‘Long Committee’ suggested that all nine counties of Ulster should be excluded,but the British Government yielded to Ulster Unionist demands for six county exclusion in the Government of Ireland Act, which passed in December 1920. The Government of Ireland Act established two separate parliaments for ‘Northern Ireland’ and ‘Southern Ireland’, and came into force on 3 May 1921. Northern Ireland encompassed the six most north-easterly counties and Southern Ireland comprised the remaining 26 counties. While almost all nationalists, both north and south, disagreed with partition and refused to participate in either parliament, most unionists within the six counties accepted the creation of Northern Ireland and worked to make it a functioning political entity.
The Anglo-Irish Treaty
The border was further solidified in late 1921 through the Anglo-Irish Treaty. Signed by a delegation of Irish nationalists and the British Government, the Treaty created the Irish Free State, which granted more independence to Ireland than through the Government of Ireland Act. Article 12 of the Treaty, however, allowed the Government of Northern Ireland to opt out of the Irish Free State, which would then trigger the formation of a Boundary Commission. The Government of Northern Ireland opted out of the Irish Free State as soon as it could, on 7 December 1922.