Sinn Fein publicly opposed partition and sought a united Ireland when Ireland was divided in 1921. It fought the first election to the Northern Ireland parliament on an anti-partitionist stance and was successful in reopening the issue of Ulster during the Treaty negotiations from October to December 1921, much to the dismay of Ulster unionists.
Its policy on partition, however, when one existed, was generally incoherent and its public commitment to a united Ireland was not matched by much of its actions in 1921.
From its rise in popularity after the 1916 Easter Rising through to 1921, other than the counter-productive Belfast Boycott, Sinn Fein had no clear policy on how to deal with the unionist minority in the north-east of Ireland. Sinn Fein leaders stuck steadfastly and naively to the view that Ulster would readily come into an all-Ireland parliament once Britain was removed from the island.
This was partly due to the party's lack of penetration in the north, clearly demonstrated by the profiles of the six Sinn Fein members elected to the northern parliament in May 1921; Eamon de Valera, Michael Collins, Arthur Griffith, Eoin MacNeill, Sean Milroy and Sean O'Mahony.
Most of them were high profile figures in the south. The main northerners in Sinn Fein were Eoin MacNeill, Ernest Blythe and Sean MacEntee.
They took an interest in the north, but their commitment was to southern politics. Sinn Fein MP for Fermanagh and Tyrone Cahir Healy attacked the party's policy towards the north in the years since 1916, "The truth is that none of the Irish leaders understood the northern situation or the northern mind".
In 1921, Sinn Fein leader de Valera moved from a stance of 'Ulster must be coerced if she stood in the way' to one of ruling out the use of force against Ulster.
This was not replaced with any meaningful policy to engage with Ulster unionists.
Strategically, Sinn Fein was all at sea on how a united Ireland could be achieved. The Ulster unionist position was greatly aided by the absence of a coherent Sinn Fein northern policy.
During the Anglo-Irish Treaty negotiations from October to December 1921, once the Sinn Fein delegation stated that its allegiance to crown and empire was contingent on Ireland's 'essential unity', Lloyd George and others within the British government appeared open to changing Northern Ireland's status.
Lloyd George unsuccessfully tried to convince the Northern Ireland prime minister James Craig into accepting an all-Ireland parliament.
Craig refused to concede any ground and instead won a major victory with Lloyd George agreeing to transfer services to Northern Ireland in November. Services such as policing, local government, agriculture and education were not transferred by the British with the birth of Northern Ireland.
The Irish delegation were aware that the northern jurisdiction was not fully functioning when the conference began in October, services being withheld demonstrated that partition could be negotiable, but they appeared unaware on how to use this to their advantage.
With the avenue of reaching a settlement by pressurising Craig now closed, Lloyd George dangled the idea of a boundary commission to Sinn Fein instead. Arthur Griffith believed there would be benefits to it, that it "would give us most of Tyrone, Fermanagh, and part of Armagh and Down".
The Anglo-Irish Treaty's main provision relating to Ulster was Article 12, stipulating that if Northern Ireland opted not to join the Irish Free State, a boundary commission would determine the border "in accordance with the wishes of the inhabitants, so far as may be compatible with economic and geographic conditions".
Central to the problem with the boundary commission was its ambiguity. No plebiscite was asked for, the clause was open to a number of different interpretations, and no time was specified for the convening of the commission.
The Sinn Fein delegation blundered greatly in acceding to such a vague and indefinable clause.
By signing the Anglo-Irish Treaty, Sinn Fein officially recognised partition but it was consoled and overly optimistic, as it would transpire, on the outcomes that would be achieved from the boundary commission.
The optimism in many ways explains the fraction of time devoted to partition (just nine out of the total 338 pages of the Treaty debates) during the acrimonious Dail Eireann debates over the Treaty. Both the pro and anti-Treaty sides supported the boundary commission as a means to an end or at least limit partition.
The split arose over sovereignty. It is astonishing that there was so little scrutiny over such a vague clause that ultimately resulted in no change to the border in 1925.
Perhaps it demonstrated that Sinn Fein's real commitment to a united Ireland was illusory and at odds with its public rhetoric.
Northern nationalists increasingly detected this waning commitment and abandonment by southern leaders, with Cahir Healy concluding that "we must look after ourselves".
Cormac Moore is author of Birth of the Border: The Impact of Partition in Ireland (Merrion Press, 2019)