It was the first general election to be held after the Representation of the People Act 1918. It was thus the first election in which women over the age of 30, and all men over the age of 21, could vote. Previously, all women and most working-class men had been excluded from voting.
In the aftermath of the elections, Sinn Féin's elected members refused to attend the British Parliament in Westminster (London), and instead formed a parliament in Dublin, the First Dáil (Irish for "Assembly"), which declared Irish independence as a republic. The Irish War of Independence was conducted under this revolutionary government which sought international recognition, and set about the process of state-building.
In 1918 the whole of Ireland was a part of the United Kingdom of Great Britain and Ireland, and was represented in the British Parliament by 105 MPs. Whereas in Great Britain most elected politicians were members of either the Liberal Party or the Conservative Party, from the early 1880s most Irish MPs were Irish nationalists, who sat together in the British House of Commons as the Irish Parliamentary Party.
The IPP strove for Home Rule, that is, limited self-government for Ireland within the United Kingdom, and had been supported by most Irish people, especially the Catholic majority. Home Rule was opposed by most Protestants in Ireland, who formed a majority of the population in the northern province of Ulster but a minority in the rest of Ireland, and favoured maintenance of the Union with Great Britain (and were therefore called Unionists).
The Unionists were supported by the Conservative Party, whereas from 1885 the Liberal Party was committed to enacting some form of Home Rule. Unionists eventually formed their own representation, first the Irish Unionist Party then the Ulster Unionist Party. Home Rule appeared to have been finally achieved with the passing of the Home Rule Act 1914. However, the implementation of the Act was temporarily postponed with the outbreak of World War I due to determined Ulster Unionists' resistance to the Act. As the war prolonged and with the failure to make any progress on the issue, the more radical Sinn Féin began to grow in strength.