The Irish Civil War began on June 28, 1922. It was fought between the provisional government of Southern Ireland (which became the Irish Free State on December 6, 1922) and the IRA members who were unwilling to accept the Anglo-Irish Treaty of December 1921, which had formally established the Irish Free State. The IRA chose to oppose the Treaty because, under it, Ireland remained part of the British Empire, an option they found unacceptable after having made a commitment to establishing the Republic of Ireland. To them, the Free Staters were breaking their oaths to uphold the Republic that had been declared in 1919 by the Dáil (revolutionary parliament).
The Civil War came on the heels of the Anglo-Irish War, which lasted from 1919 until 1921. This war had been fought by the IRA, which was heavily influenced by the leadership of the Irish Republican Brotherhood (IRB). The mastermind behind the IRA’s terror campaign against the British and their supporters was Michael Collins, the Minister of Finance for the Dáil, Director of Intelligence for the IRA, and President of the IRB. This was the birth of modern guerilla warfare and it was terribly effective. The war ended on July 11, 1921 with a truce between the British and the IRA. By December the two sides had negotiated the treaty whereby the 26 southern counties formed their own government, separate from direct British rule. The 6 counties that now make up Northern Ireland were given the option of joining the Free State; the decision to remain separate was controversial, but the British obviously did not object to the Treaty not being fully followed.
The sticking point for the IRA’s members was the oath of allegiance Irish citizens would have to swear to the British crown; Ireland would remain part of the Empire. They had fought to establish the Republic in a unified Ireland, not to see it partitioned and under foreign rule. The Free Staters argued that they could not possibly win a longer war against Britain and that the establishment of the Free State was the first step towards the establishment of the Republic. Historians have since described this of a clash of idealism against pragmatism.
The IRA was led by Éamon de Valera, the President of the Republic of Ireland that had been declared in 1919. It seems that, to some degree, he was overwhelmed by events. He had ordered the delegates sent to Britain to negotiate the treaty to send the terms to him for review before signing the Treaty; they did not. Upon their return, the Treaty was ratified by the Dáil (revolutionary parliament) and Arthur Griffith, one of the lead negotiators, was elected President. Michael Collins became Chairman of the Provisional Government and Commander-in-Chief of the National Army. It does not seem that de Valera wanted civil war, but he was unable to stop it.
On April 14, 1922, 200 members of the IRA seized the Four Courts building in Dublin. Collins wanted to avoid civil war at all costs, but with the British threatening military action if he did not act, Collins was forced to begin bombarding the Four Courts building in June 28th, beginning the Civil War.
On August 12, 1922, Arthur Griffith died of heart failure. On August 22, Collins was assassinated while attempting to negotiate a peace between the provisional government and the IRA. It was not until May 24, 1923 that the IRA finally laid down their arms and surrendered. Somewhere between 2,800 and 3,800 combatants were killed, as well as an unknown number of civilians. In 1932, de Valera became Prime Minister of the Free State and set in motion the events that would lead to the establishment of the Republic of Ireland in 1937. The Free Staters had been correct in 1922; the Anglo-Irish Treaty had led directly to the realization of the Republic of Ireland. However, many of the authors of that treaty did not live to see their dream realized.