Question: 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? 

Context paragraphs:
Repartition of Ireland: The repartition of Ireland has been suggested as a possible solution to the continuing political disagreement in Northern Ireland.  The essential problem was that the partition of Ireland was gerrymandered, and as a result Northern Ireland contains a large Irish nationalist minority.  Much of the Irish nationalist population lives in the south and west of the region, but a significant percentage lives in Belfast and some smaller communities in the north and east, whilst Irish unionists constitute a majority of the population in the north and east of the region with some smaller communities in the south and west.  The geographical area in which unionists are a majority is less than half of Northern Ireland (see graphic below), but eastern areas have a much higher population density.  Collectively, Northern Ireland is split, with unionists comprising approximately 48% of the population, and falling quickly.  At the last general election unionists secured precisely 50% of the seats.  None of these proposals are currently supported by any political party in Ireland.

Maud Gonne: Maud Gonne MacBride (Irish: "Maud Nic Ghoinn Bean Mac Giolla Bhríghde" , 21 December 1866 – 27 April 1953) was an English-born Irish revolutionary, suffragette and actress.  Of Anglo-Irish stock and birth, she was won over to Irish nationalism by the plight of evicted people in the Land Wars.  She also actively agitated for Home Rule.

Pan-Celticism: Pan-Celticism or Celtic nationalism is a political, social and cultural movement advocating solidarity and cooperation between Celtic nations (both the Gaelic and Brythonic branches) and the modern Celts in North-Western Europe.  Some pan-Celtic organisations advocate the Celtic nations seceding from the United Kingdom and France and forming their own separate federal state together, while others simply advocate very close cooperation between independent sovereign Celtic nations, in the form of Irish nationalism, Scottish nationalism, Welsh nationalism, Breton nationalism, Cornish nationalism and Manx nationalism.

Young Ireland: Young Ireland (Irish: "Éire Óg" , ] ) was a political, cultural and social movement of the mid-19th century.  It began as a tendency within Daniel O'Connell's Repeal Association, associated with "The Nation" newspaper, but eventually split to found the Irish Confederation in 1847.  Young Ireland led changes in Irish nationalism, including an abortive rebellion known as the Young Irelander Rebellion of 1848.  Many of the rebellion's leaders were tried for sedition and sentenced to penal transportation to Van Diemen's Land.  From its beginnings in the late 1830s, Young Ireland grew in influence and inspired following generations of Irish nationalists.  Some of the junior members of the movement went on to found the Irish Republican Brotherhood.

United Ireland: United Ireland is the proposition that the whole of Ireland should be a single sovereign state.  At present, the island is divided politically; the sovereign state of Ireland has jurisdiction over the majority of Ireland, while Northern Ireland is part of the United Kingdom.  Achieving a united Ireland is a central tenet of Irish nationalism, particularly of both mainstream and dissident Irish republican political and paramilitary organisations.  Unionists support Northern Ireland remaining part of the United Kingdom, and therefore oppose Irish unification.

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.  It was the dominant political movement of Irish nationalism from 1870 to the end of World War I.

Two nations theory (Ireland): In Ireland, the two nations theory holds that Ulster Protestants form a distinct Irish nation.  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.

Taiwanese nationalism: Taiwanese nationalism () is a nationalist political movement to unite residents of Taiwan as a nation and eliminate the current political and social division of Taiwan's people on the issues of national identity, the "Chinese reunification" vs. "independence" debate, and resolving the political status of Taiwan and its political dispute with China.  It is closely linked to Taiwan independence but distinguished from it in that the independence movement seeks to eventually establish an independent "Republic of Taiwan" in place of or out of the Republic of China and obtain United Nations and international recognition as a sovereign state (country), while the nationalism movement seeks only to establish or reinforce an independent Taiwanese identity that distinguishes Taiwan's people apart from Chinese nationalism, without necessarily advocating changing the official name of the Republic of China to "Republic of Taiwan".

History of Ireland (1801–1923): Ireland was part of the United Kingdom of Great Britain and Ireland from 1801 to 1922.  For almost all of this period, the island was governed by the UK Parliament in London through its Dublin Castle administration in Ireland.  Ireland faced considerable economic difficulties in the 19th century, including the Great Famine of the 1840s.  The late 19th and early 20th centuries saw a vigorous campaign for Irish Home Rule.  While legislation enabling Irish Home Rule was eventually passed, militant and armed opposition from Irish unionists, particularly in Ulster, opposed it.  Proclamation was shelved for the duration following the outbreak of World War I.  By 1918, however, moderate Irish nationalism had been eclipsed by militant republican separatism.

Protestant Irish nationalists: Protestant Irish nationalists refers to adherents of Protestantism in Ireland who also support Irish nationalism.  Protestants have played a rather large role in the development of Irish nationalism since the eighteenth century, despite most Irish nationalists historically being from the Irish Catholic majority, as well as most Irish Protestants usually tending toward unionism in Ireland.  Protestant nationalists (or "patriots", particularly before the mid-19th century) have consistently been influential supporters and leaders of various movements for the political independence of Ireland from Great Britain.  Historically, these movements ranged from supporting the legislative independence of the Parliament of the Kingdom of Ireland; to a form of home rule within the United Kingdom of Great Britain and Ireland, to complete independence in an Irish Republic, and (since the partition of Ireland) a United Ireland.

Supporting paragraphs: Two nations theory (Ireland) Irish Home Rule movement
Answer: the end of World War I.