The Anglo-Irish Treaty signed on 6 December 1921 ended this war by granting most of the island a great degree of independence, but with six counties in the north staying within the United Kingdom as the new jurisdiction of Northern Ireland.

[1][2] Óglaigh na hÉireann was also adopted as the name of the pro-Treaty National Army, and it remains the official legal title of the Irish Defence Forces.

[3] The signing of the Anglo-Irish Treaty by the Irish delegation in London caused an angry reaction among the less compromising elements in Sinn Féin and among a majority of the IRA.

[citation needed] In March 1922, the Anti-Treaty IRA captured the Royal Navy vessel Upnor off the coast of Cobh, County Cork, which was carrying arms.

At the start of the war, they had just under 7,000 rifles, a few machine guns and a handful of armoured cars taken from British garrisons (who were under orders not to fire on IRA units) as they evacuated the country.

Confused fighting raged for another five days, with anti-Treaty elements of the IRA's Dublin Brigade, under Oscar Traynor, occupying O'Connell Street until they were dislodged by artillery fire.

Only in County Kerry was a relatively effective campaign fought, with the IRA units re-taking Kenmare and other towns from the Free State on several occasions.

"[9] By this time, thousands of republicans were already prisoners of the Free State government led by W. T. Cosgrave; many more were arrested after they dumped arms and returned to civilian life.

The casualties of the anti-Treaty IRA in the Civil War have never been accurately counted, but are thought to have been considerably more than the 800 or so deaths suffered by the Free State Army, perhaps two or three times as numerous.

The period immediately following the Irish Civil War saw the IRA swing towards the political left, manifest in the election of Moss Twomey to the position of chief of staff.

Under his reign, he cautiously opened the IRA up to left-wing influences in order to contrast it against the emerging right-wing stance of the Cumann na nGaedheal government.

[10] The pact was originally approved by Frank Aiken, who left soon after to co-found Fianna Fáil with De Valera, before being succeeded by Andrew Cooney and Moss Twomey, who kept up the secret IRA-Soviet espionage relationship until around 1930–31.

[10] While Twomey was not an ideological Marxist-Leninist (although there were some communists in the IRA at this time, such as Peadar O'Donnell), he saw the arrangement as purely utilitarian and regarded the Soviets as "shifty" and "out to exploit us.

Political initiatives such as Saor Éire, begun in 1931, were promoted by left-wing IRA members such as George Gilmore, Peadar O'Donnell and Frank Ryan.

In the years after the Civil War, many republicans viewed the Free State, with its censorship of newspapers and extensive coercive legislation, as a sham democracy, in the service of British imperialism.

Another important factor was the formation of the Blueshirts: a quasi-fascist organisation set up by Eoin O'Duffy, originally composed of Civil war veterans of the Free State Army.

Initially, de Valera's Fianna Fáil government was friendly towards the IRA, legalising the organisation and freeing all their prisoners who had been interned by Cumann na nGaedhael.

De Valera banned the IRA in 1936, after they murdered a landlord's agent, Richard More O'Farrell, in a land dispute and fired shots at police during a strike of Dublin tramways workers, on top of their bank robberies.

In 1931 Saor Éire had quickly collapsed due to the combination of fierce reaction from the Catholic Church, deeply hostile to anything that appeared communist, and repressive legislation immediately introduced by the government.

(At the same time, IRA opponent and Greenshirts leader Eoin O'Duffy organised the Irish Brigade to go to Spain to fight on the opposing side, with Francisco Franco's Nationalists.)

Barry began preparations for a large-scale invasion of Northern Ireland, establishing camps where hundreds of IRA men were trained, creating detailed maps containing the locations of army and police barracks, and importing Thompsons with the help of Clan na Gael.

7 of these former TDs transferred what authority they believed they had as representatives of the second Dáil to the IRA army council, thus, in their minds, rendering it the legitimate governing body of Ireland.

[22] In 1939 O'Donovan became increasingly enamoured of Nazi ideology and visited Germany three times ‘to discuss potential agents, the supply of arms in the event of war, [and to collect] radio sets and courier communication.

While O'Duffy did not take up the offer, he was later invited to join Moss Twomey and Andrew Cooney in protesting the basing of American troops in Northern Ireland.

[24] In 1940, prominent members and supporters of the IRA established Córas na Poblachta, which, among its objectives, called for the "destruction of the Masonic Order in Ireland" and the "reversal of the cultural conquest of our country by England", not excluding "the employment of compulsion" to that end.

On 23 December 1939, IRA members stole almost the entire reserve ammunition store of the Irish Army from the Magazine Fort in Dublin's Phoenix Park.

[21] When George Bernard Shaw retorted that the Nazis were anti-Catholic, the IRA responded that Hitler's and Mussolini's support of Franco in Spain proved their pro-Catholic credentials.

[34] But while Graham, who opposed cooperation with the Germans, and others in the Belfast command continued to debate the merits of a new northern campaign, in April 1942 a diversionary action, intended to draw the RUC from an illegal 1916 commemoration, developed into a street gun battle.

that during the war period IRA members may have attempted to provide intelligence to assist the German aerial bombing of industrial targets in Northern Ireland.

[46] The move to a class-based political outlook and the consequent rejection of any stance that could be seen as sectarian—including the use of IRA arms to defend one side, that side being the beleaguered Catholic communities of Belfast in the Northern Ireland riots of August 1969—was to be one of the factors in the 1969 split that led to the Provisional IRA wing of the republican movement, with the latter subscribing to a traditional Catholic/nationalist analysis of the situation while the Officials subscribed to the Marxist view that internal strife among the working classes served only the interest of capital.