Sinn Féin contested the general election of 1918 on the platform that instead of taking up any seats they won in the United Kingdom Parliament, they would establish a revolutionary assembly in Dublin.
In republican theory every MP elected in Ireland was a potential Deputy to this assembly.
A letter from Thomas Harbison, MP was read to the revolutionary Dáil Éireann on 22 January 1919.
He expressed his entire sympathy with the demand of Ireland for a hearing of her just Cause at the Congress of the Nations.
In 1921 Sinn Féin decided to use the UK authorised elections for the Northern Ireland House of Commons and the House of Commons of Southern Ireland as a poll for the Irish Republic's Second Dáil.