A united Ireland is a proposition that the whole of Ireland should be a single sovereign state. At present, the island is divided politically; the sovereign state of Ireland, or the Republic of Ireland, has jurisdiction over the majority of the island 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 and Ulster loyalists support Northern Ireland remaining part of the United Kingdom, and therefore oppose Irish unification.
Ireland has been partitioned since May 1921, when the implementation of the Government of Ireland Act 1920 created the state of Northern Ireland within the United Kingdom. The Anglo-Irish Treaty, by which the Irish Free State became independent, recognised partition, but this was opposed by anti-Treaty republicans. When the anti-Treaty Fianna Fáil party came to power in the 1930s, it adopted a new constitution which claimed sovereignty over the entire island. The Irish Republican Army (IRA) had a united Ireland as its goal during the thirty-year conflict with British security forces known as The Troubles. The Good Friday Agreement of 1998, which ended the conflict, acknowledged the legitimacy of the desire for a united Ireland, as well as the desire of unionists for the maintenance of the union with Britain. In 2016, Sinn Féin called for a referendum on a united Ireland in the wake of the decision by the United Kingdom to leave the European Union (EU). Taoiseach (Irish head of government) Enda Kenny said that in the event of reunification Northern Ireland should be allowed to rejoin the EU along with the Republic.