Irish Civil War

The Irish Civil War, fought from 28 June 1922 to 24 May 1923, was a defining conflict in the political and military history of modern Ireland. It erupted in the aftermath of the Irish War of Independence and accompanied the formation of the Irish Free State, a self-governing dominion within the British Empire. The war was rooted in a fundamental disagreement over the Anglo–Irish Treaty, which ended the conflict with Britain but divided the nationalist movement. Former comrades in the struggle for independence found themselves on opposing sides, leading to a conflict that shaped political alignments in Ireland for generations.

Background to the Conflict

The Anglo–Irish Treaty, signed in December 1921, brought an end to the War of Independence by establishing the Irish Free State with its own army, police force, and legislative autonomy. The Treaty also allowed Northern Ireland, comprising six counties with a Protestant majority, to opt out of the new state, a decision it exercised immediately. This confirmed the existing partition arrangements and formalised British authority in the north.
The terms of dominion status were contentious. Although similar to the constitutional position of Canada or Australia, many Irish republicans objected to the continued role of the British monarch as head of state and to the requirement that members of the new Free State parliament swear an Oath of Allegiance. The retention by Britain of several strategic Treaty Ports further fuelled opposition among those who believed the Treaty fell short of full independence.
While Michael Collins argued that the agreement provided the “freedom to achieve freedom”, many others considered it a fundamental betrayal of the republic declared during the Easter Rising and ratified by the Dáil in 1919. Central to this dispute was the disestablishment of the Irish Republic and the belief among anti-Treaty forces that acceptance of the agreement undermined the legacy of those who had fought and died for Irish self-determination.

Political Division and the Treaty Split

The Treaty split the nationalist movement at every level. Not only were political leaders divided, but many had also been close comrades during the War of Independence. Personal and ideological tensions deepened the rift. The Dáil approved the Treaty by a narrow margin of 64 to 57 votes in January 1922. Following its ratification, Éamon de Valera resigned as President of the Irish Republic and was not re-elected, further tightening political divisions.
De Valera’s opposition included proposals for an alternative arrangement known as “external association”, in which Ireland would remain linked to the Commonwealth without full membership. This suggestion gained little traction. During a speaking tour in Munster in March 1922, his speeches—suggesting that acceptance of the Treaty would lead to Irish people fighting “Irish soldiers of an Irish government”—provoked controversy and reflected the depth of his objections.
Military divisions mirrored political ones. Many officers in the Irish Republican Army rejected the Treaty, arguing that the Dáil acted beyond its authority in accepting it. By March 1922, a faction of anti-Treaty IRA leaders formed their own Army Executive, declaring themselves the legitimate government. Meanwhile, the Provisional Government, established under the Treaty’s terms, worked to assume administrative control as British forces prepared to withdraw.

Outbreak of the Civil War

Tensions escalated through the spring of 1922 as rival groups competed for authority and legitimacy. Anti-Treaty IRA members occupied key buildings in Dublin, while sporadic violence and armed raids occurred throughout the country. The Provisional Government sought to assert central authority, insisting that the Treaty mandated a recognised political structure.
The conflict formally began in late June 1922 when National Army forces attacked anti-Treaty units entrenched in Dublin. The initial confrontation, known as the Battle of Dublin, resulted in the Provisional Government securing control of the capital by early July. This marked a decisive shift, allowing the National Army to deploy its growing resources across the country.

Course of the War

With significant quantities of arms supplied by the British government, including artillery and armoured vehicles, the National Army launched a series of offensives. By August 1922, they had captured urban centres across southern and western Ireland, effectively dismantling the anti-Treaty strongholds collectively referred to as the “Munster Republic”.
Despite these setbacks, anti-Treaty forces reorganised into smaller guerrilla units, adopting tactics similar to those used against British forces during the War of Independence. This phase of the conflict—characterised by ambushes, raids, and sabotage—continued for approximately ten months. However, with diminishing supplies, declining public support, and increasing pressure from National Army units, the anti-Treaty campaign gradually lost coherence.
In April 1923, following sustained military losses and the death or capture of several prominent leaders, the anti-Treaty IRA Executive issued an order instructing volunteers to “dump arms”, effectively ending organised resistance. Although this statement did not concede defeat formally, it signalled the end of the civil war.

Consequences and Legacy

The Irish Civil War left deep wounds in Irish society. The conflict strained relationships among families, communities, and former comrades, generating a bitterness that persisted for decades. The National Army emerged as the official military force of the newly established Free State, while anti-Treaty republicans faced imprisonment, execution, and political marginalisation.
The Treaty split had long-lasting political consequences. Three of the modern Republic of Ireland’s largest political parties trace their origins to opposing sides in the conflict: Fine Gael from pro-Treaty supporters, Fianna Fáil from the majority of anti-Treaty republicans under de Valera, and Sinn Féin from a minority who refused to join any party accepting partition or the legitimacy of the Free State.
The war also cemented the political and territorial division of the island. Northern Ireland remained within the United Kingdom, while the Free State continued on a gradual path toward fuller sovereignty, eventually becoming a republic in 1949.