Irish unionists use the two nations theory as a basis for opposing a movement that agitated for self-government that was the dominant political movement of Irish nationalism until when? 
Two nations theory (Ireland): In Ireland, the two nations theory holds that Ulster Protestants form a distinct Irish nation. Two nations theory (Ireland):  Advocated mainly by Irish unionists, who used it as a basis for opposing Home Rule and, later, to justify the partition of Ireland, it has been strongly criticised by Irish nationalists such as John Redmond (who stated that "'the two nation theory' is to us an abomination and a blasphemy"), Éamon de Valera, Seán Lemass and Douglas Gageby. Irish Home Rule movement: The Irish Home Rule movement was a movement that agitated for self-government for Ireland within the United Kingdom of Great Britain and Ireland. Irish Home Rule movement:  It was the dominant political movement of Irish nationalism from 1870 to the end of World War I.
the end of World War I.