The Anglo-Irish Treaty, which led to the establishment in December 1922 of a dominion called the Irish Free State, recognised partition, but this was opposed by anti-Treaty republicans.
The Irish Republican Army (IRA) had a united Ireland as its goal during the conflict with British security forces and loyalist paramilitaries from the 1960s to the 1990s known as The Troubles.
The Good Friday Agreement signed in 1998, which ended the conflict, acknowledged the legitimacy of the desire for a united Ireland, while declaring that it could be achieved only with the consent of a majority of the people of both jurisdictions on the island, and providing a mechanism for ascertaining this in certain circumstances.
[23] This provision was introduced in 1999 after implementation of the Good Friday Agreement, as part of replacing the old Articles 2 and 3, which had laid a direct claim to the whole island as the national territory.
In 1886, Parnell formed a parliamentary alliance with Liberal Party Prime Minister William Ewart Gladstone and secured the introduction of the First Home Rule Bill.
"[39] Lynch renewed his call to end partition in August 1969 when he proposed negotiations with Britain with the hope of merging the Irish Republic and Northern Ireland into a federal type state.
The next day the Northern Prime Minister Brian Faulkner rejected Lynch's statement and stated that "no further attempt by us to deal constructively with the present Dublin government is possible.
"[41] Later in 1971 British Labour Party leader (and future Prime Minister) Harold Wilson proposed a plan that would lead to a united Ireland after a 15-year transitional period.
The Provisional Irish Republican Army (IRA) had begun a thirty-year campaign against British security forces with the aim of winning a united Ireland.
[43] In 1970, the Social Democratic and Labour Party (SDLP) was established to campaign for civil rights and a united Ireland by peaceful, constitutional means.
The freedom of movement, allowed citizens of either jurisdiction to live in which ever part of the island they wanted, therby enabling them to choose which state they paid taxes to or claimed benefits from.
[51] The status and treatment of Northern Ireland and Gibraltar, the only parts under control of the United Kingdom which would have new land borders with the EU following the UK withdrawal, became important to the negotiations, along with access to the regional development assistance scheme (and new funding thereof) from the European Union.
[62] The 2020 Brexit withdrawal agreement included the Northern Ireland Protocol, which established different trade rules for the territory than Great Britain.
[63] The new UK prime minister Boris Johnson continued to claim no trade border would take form as late as August 2020, despite having negotiated its creation.
The implementation of the protocol, and the new regulatory hurdles had a negative effect on east–west trade, and drew strong condemnation from unionist figures, including DUP members such as First Minister Arlene Foster.
[69] In February 2021, several unionist parties began a legal challenge, alleging that the protocol violated the Act of Union 1800, the bill which had originally merged Ireland with the United Kingdom, as well as the Good Friday Agreement.
[73] The Irish Times interviewed loyalist Shankill Road residents that month and found significant anger at the DUP, and accusations that the community had been "sold short" on the protocol.
[82] On 31 January 2024, a deal between the DUP and the UK government led to the abolition of "routine" checks on goods from Britain sent to Northern Ireland with the intention of staying there.
[84] After taking office as First Minister, O'Neill stated that she expected a referendum on the reunification to be held within the next decade, which would be in accordance with the 1998 Good Friday Agreement signed by the UK and Ireland.
[86] In February 2024, it was announced that a total of €1 billion of funding from the Irish government was committed for: The Narrow Water bridge, linking Omeath to Warrenpoint, began construction in June 2024.
[90] In 2020, Ireland Taoiseach Micheál Martin said that a referendum on Irish unity should not be held for 5 years, adding, "once Brexit happened, it should not be a catalyst for something like a border poll.
[95] First minister elect, Michelle O’Neill launched Sinn Fein's manifesto at the Canal Court Hotel in Newry in March 2023 which was a 16-page document including a commitment to set a date on a unity referendum.
On 4 February, the day after becoming First Minister, Michelle O'Neill contested this, outlining her vision of a "decade of opportunity"; in other words, a border poll could be held in 10 years.
When asked about the criteria, Northern Ireland secretary Chris Heaton-Harris said that those interested “need to read the Belfast/Good Friday Agreement, it’ll give you a good clue”.
[105] Ian Paisley Jr. suggested that support to unify Ireland is not adequate and that should a vote come about, a supermajority and a turnout quota should be required for a border poll.
The initial party constitution of Fianna Fáil in 1926 under Éamon de Valera included as the first of its aims, "To secure the Unity and Independence of Ireland as a Republic".
Fianna Fáil leaders Albert Reynolds and Bertie Ahern led Irish governments in favour of the Downing Street Declaration and the Good Friday Agreement respectively.
Its Éire Nua (in English, New Ireland) policy advocates a unified federal state with regional governments for the four provinces and the national capital in Athlone.
They cite lower paid and less secure jobs in the North and say that a United Ireland would allow for a more coordinated economic strategy and increasing investment, productivity and improving infrastructure, particularly in the border region.
They cite the decline of the small Protestant population of the Republic of Ireland since independence from the United Kingdom, the economic cost of unification, their place in a key international player within the UK and their mainly non-Irish ancestry.