The anti-treaty IRA fought a civil war against the Free State Army in 1922–1923, with the intention of creating a fully independent all-Ireland republic.

At the army convention held in Dublin in October 1917, Éamon de Valera was elected president, Michael Collins Director for Organisation and Cathal Brugha Chairman of the Resident Executive, which in effect made him Chief of Staff.

[6] Already in September 1917, a group of men from counties Clare and Tipperary charged with illegal drilling were claiming to be soldiers of the "Irish Republican Army" and refused to recognise the legitimacy of the court, and insisted they should be treated as prisoners of war.

Brugha was nominally the superior as Minister for Defence, but Collins's power base came from his position as Director of Organisation of the IRA and from his membership on the Supreme Council of the Irish Republican Brotherhood (IRB).

De Valera resented Collins's clear power and influence, which he saw as coming more from the secretive IRB than from his position as a Teachta Dála (TD) and minister in the Aireacht.

Brugha and de Valera both urged the IRA to undertake larger, more conventional military actions for the propaganda effect but were ignored by Collins and Mulcahy.

Moreover, many members of the Dáil, notably Arthur Griffith, did not approve of IRA violence and would have preferred a campaign of passive resistance to the British rule.

[8] These men were able to issue orders and directives to IRA guerrilla units around the country and at times to send arms and organisers to specific areas.

However, because of the localised and irregular character of the war, they were only able to exert limited control over local IRA commanders such as Tom Barry, Liam Lynch in Cork and Seán Mac Eoin in Longford.

[9] The IRA distrusted those Irishmen who had fought in the British Army during the First World War as potential informers, but there were a number of exceptions such as Emmet Dalton, Tom Barry and Martin Doyle.

[10] A disproportionate number of the "active" IRA men were teachers, medical students, shoemakers and bootmakers; those engaged in building trades like painters, carpenters and bricklayers; draper's assistants and creamery workers.

[13] Those Irishmen engaged in white-collar trades or working as skilled labourers were much more likely to be involved in cultural nationalist groups like the Gaelic League than farmers or fishermen, and thus to have a stronger sense of Irish nationalism.

Thus, those engaged in Irish nationalist activities in urban areas were much more likely to come into conflict with the Crown, leading to a greater chance of radicalisation.

[18] The majority of the IRA men operating in Britain were Irish-born, but there was a substantial minority who were British-born, something that made them especially insistent on asserting their Irish identity.

[citation needed] The second phase of the IRA campaign, roughly from January to July 1920, involved attacks on the fortified police barracks located in the towns.

Thus, the third phase of the war (roughly August 1920 – July 1921) involved the IRA taking on a greatly expanded British force, moving away from attacking well-defended barracks and instead using ambush tactics.

For instance, the County Longford IRA under Seán Mac Eoin carried out a number of well-planned ambushes and successfully defended the village of Ballinalee against Black and Tan reprisals in a three-hour gun battle.

The IRA in Belfast and the North generally, although involved in protecting the Catholic community from loyalists and state forces, undertook a retaliatory arson campaign against factories and commercial premises.

By the end of the war in July 1921, the IRA was hard-pressed by the deployment of more British troops into the most active areas and a chronic shortage of arms and ammunition.

Towards the end of the war, some Thompson submachine guns were imported from the United States; however 495 of these were intercepted by the American authorities and the remainder only reached Ireland shortly before the Truce.

The Church of Ireland Gazette recorded numerous instances of Unionists and Loyalists being shot, burnt or forced from their homes during the early 1920s.

"[25] Many historic buildings in Ireland were destroyed during the war, most famously the Custom House in Dublin, which was disastrously attacked on de Valera's insistence, to the horror of the more militarily experienced Collins.

In this regard, the IRA acted to a large degree as an agent of social control and stability, driven by the need to preserve cross-class unity in the national struggle,[26] and on occasion being used to break strikes.

An unexpected olive branch came from King George V, who, in a speech in Belfast called for reconciliation on all sides, changed the mood and enabled the British and Irish Republican governments to agree to a truce.

On 8 July, de Valera met General Nevil Macready, the British commander in chief in Ireland and agreed terms.

Partition was not by itself the key breaking point between pro- and anti-Treaty campaigners; both sides expected the Boundary Commission to greatly reduce Northern Ireland.

The majority of the IRA rank-and-file were against the Treaty;[30] in January–June 1922, their discontent developed into open defiance of the elected civilian Provisional government of Ireland.

A month later, on 18 February, Liam Forde, O/C of the IRA Mid-Limerick Brigade, issued a proclamation stating that: "We no longer recognise the authority of the present head of the army, and renew our allegiance to the existing Irish Republic".

On 22 March, Rory O'Connor held what was to become an infamous press conference and declared that the IRA would no longer obey the Dáil as (he said) it had violated its Oath to uphold the Irish Republic.

The IRA of the Civil War and subsequent organisations that have used the name claim lineage from that group, which is covered in full at Irish Republican Army (1922–1969).