Former taoiseach Leo Varadkar suggested that people in the Republic of Ireland may one day need to apologise for abandoning northern nationalists after partition a century ago. Speaking in Dungannon, he said the southern state went off and built itself while largely forgetting about events in the North for a long time.

Varadkar did not specify what actions should be included in an apology. Historical analysis shows that partition was imposed by Westminster through the Government of Ireland Act 1920 without consultation or votes from Irish nationalists, apart from a small number of Irish Parliamentary Party MPs. By the time the Anglo-Irish Treaty talks began in 1921, London made clear that Northern Ireland's status was not negotiable.

Arthur Griffith secured a Boundary Commission to redraw the border according to residents' wishes, with the expectation that it would make Northern Ireland unviable. However, the commission proved a disappointment for nationalists. The Cumann na nGaedheal government appointed Eoin MacNeill, who was not effective in the negotiations. When the commission's findings leaked in November 1925, they showed only minor adjustments and even some transfers of territory from the Free State. The government sought to suppress the report and accepted a British offer to write off Ireland's share of the imperial debt in exchange for keeping the border unchanged. That debt equalled about 80 percent of the new state's annual GDP.

In 1923, the Free State government reinforced the hard border by establishing customs posts. This decision was partly to raise revenue and assert sovereignty, but it made partition a daily reality for border communities on both sides of the religious divide who did not wish to be divided.

After that, William T Cosgrave and northern prime minister James Craig did not meet again. The leaders of the two jurisdictions would not meet for 40 years until Seán Lemass and Terence O'Neill met in Stormont Castle in January 1965.

Fianna Fáil under Éamon de Valera was more focused on the issue. The 1937 constitution contained articles claiming jurisdiction over the whole island. In 1938, during talks with Neville Chamberlain, a declaration was discussed that Britain had no selfish interest in Northern Ireland, but it was derailed by the IRA's bombing campaign in 1939 and the second World War. In 1940, de Valera rejected Winston Churchill's offer to end partition in return for Ireland entering the war, believing the promise would not be kept.

Later, a coalition government led by John A Costello funded nationalist candidates in Northern Ireland elections. This move backfired by uniting unionists around the Ulster Unionist Party in the 1949 Stormont elections.

Lemass viewed partition differently from de Valera. He saw it as an issue between nationalists and unionists rather than solely caused by Britain. Lemass and O'Neill set aside partition to work on practical matters. However, the Troubles began in 1969, and Jack Lynch's "standing idly by" speech raised expectations that were not met by military capability.

Successive Irish governments were involved in peace efforts including Sunningdale, the Anglo-Irish Agreement, the 1993 Framework Document, and the 1998 Belfast Agreement. Varadkar himself used EU support to prevent a hard border after Brexit, and current taoiseach Micheál Martin established the Shared Island fund.

A debate continues over what the southern state could have done differently given the military and political constraints of the time.