The 1921 Irish elections took place in Ireland on 24 May 1921 to elect members of the House of Commons of Northern Ireland and the House of Commons of Southern Ireland. These legislatures had been established by the Government of Ireland Act 1920, which granted Home Rule to a partitioned Ireland within the United Kingdom.
The Ulster Unionist Party (UUP) won a landslide majority in Northern Ireland. In the area designated as Southern Ireland, Sinn Féin candidates were elected unopposed in 124 of the 128 seats. 
Only the Northern Ireland House of Commons actually sat as a functional body; the Sinn Féin candidates elected across Ireland boycotted both institutions, and instead assembled as the Second Dáil.
Background.
On 21 January 1919, the Sinn Fein MPs elected to the British House of Commons at the 1918 general election met as Dáil Éireann and declared independence from the United Kingdom. This declaration was followed by the Irish War of Independence, which continued until a truce in July 1921.
In November 1920, the British Parliament passed the Government of Ireland Act 1920. This partitioned Ireland into two distinct polities, each with their own Home Rule Parliament: Northern Ireland and Southern Ireland. Both parliaments would be composed of a directly-elected House of Commons and an indirectly-elected Senate, with both lower chambers being elected by the Single Transferable Vote system of proportional representation.
When the date of the elections was announced in the House of Commons, the Conservative MP Sir William Davison, who had been born in Broughshane, County Antrim, had asked "What is the object of holding elections in Southern Ireland when any candidates who do not support Sinn Fein would be shot?" Other members replied "How do you know?"
John Dillon and T. P. O'Connor both agreed that the Irish Party should not fight Sinn Féin for seats for the Southern parliament as things stood. Former Irish Parliamentary Party MP Stephen Gwynn, now a member of the Irish Dominion League, advocated putting up League candidates against Sinn Féin. In early March he met with southern Unionists Viscount Midleton and Lord Oranmore, requesting them to pool their resources to contest the election and contest the election on a platform opposing the IRA's violence, under Midleton's leadership. Midleton declined the invitation, just as he had declined a previous request for his Unionist Anti-Partition League to join the Dominion League.
Results.
Southern Ireland.
In the area designated as Southern Ireland, no actual polling took place as all 128 candidates were returned unopposed. Of these, 124 were won by Sinn Féin and four by independent Unionists representing Dublin University (Trinity College).
A single Unionist candidate had been selected to contest the constituency of Donegal: Major Robert L Moore, who had contested East Donegal in 1918. Moore however later withdrew his candidacy just before the election.
Northern Ireland.
The general election to the Northern Ireland House of Commons occurred on Tuesday, 24 May. Of 52 seats, including Queen's University of Belfast, 40 were won by Unionists, 6 by the Nationalist Party and 6 by Sinn Féin. Several well known republicans were elected: Éamon de Valera for South Down, Michael Collins for Armagh, Eoin MacNeill for Derry and Arthur Griffith for Fermanagh and Tyrone. Voters in Fermanagh and Tyrone returned an anti-partition majority of 7,831. Allegations were made claiming intimidation of Nationalist voters, arrests of candidates/organisers and the seizure of electoral literature.
Second Dáil.
Although the elections were formally for two separate legislatures, Irish republicans considered all those elected to be members of the Second Dáil. The composition of the Dáil following these elections was therefore as follows:
In practice, however, the Dáil was composed of 125 Sinn Fein members. The Unionist and Nationalist Party members ignored the invitation to attend the Dáil, while the four independent unionists assembled as the Southern Ireland Commons for a single brief meeting.
Aftermath.
The Northern Ireland House of Commons continued to function as a Home Rule legislature until it was abolished in 1973. The Southern Ireland Commons was largely ignored, and only formally met twice: first in a brief 1921 session that only the four unionists attended, and then again in 1922 to approve the Anglo-Irish Treaty which established the Irish Free State.
References.
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