On December 6th 1921, The Anglo-Irish Treaty effectively separated Ireland from the United Kingdom. The treaty ended the three year war for independence that gave birth not only to Ireland as a free state, but also the infamous IRA, which still continues today in a more unofficial form.
The Irish War of Independence was a guerrilla campaign that began in 1919, after the creation of the “First Dail,” the first Irish parliament that declared itself separate from Britain. The parliament ordered the formation of the Irish Republican Army (IRA) whose mandate it was to fight the “Dublin Castle British Administration” in pursuit of true freedom.
Over the course of the next two years, the IRA launched numerous attacks on key British forces, the major target being the Royal Irish Constabulary, who were seen as the incarnation of the British government in Ireland. Apart from some minor police presence, the British government didn’t respond militarily until March of 1920, with the deployment of seven thousand British World War I paramilitary veterans.
Violence continued, with attacks reaching as far as Glasgow, until 1921, when the battle effectively came to a standstill. A truce began on July 11 in 1921, and peace talks began, which led to the Anglo-Irish treaty. Under the treaty, Ireland received independence from the British government, though under the terms that Northern Ireland would be allowed to withdraw from the Irish Free State.
Despite some opposition, the treaty was agreed to, and signed on December 6 1921. Ireland, with the exception of Northern Ireland, became a unified Free State one year after, on December 6 1922.