Excerpts from Books and Wikipedia
"The Irish Free State (…) was a state established in 1922 under the Anglo-Irish Treaty of December 1921. That treaty ended the three-year Irish War of Independence between the forces of the self-proclaimed Irish Republic, the Irish Republican Army (IRA), and British Crown forces. . . . In the first months of the Free State, the Irish Civil War was waged between the newly established National Army and the anti-Treaty IRA, who refused to recognise the state. The Civil War ended in victory for the government forces, with the anti-Treaty forces dumping their arms in May 1923. . . . The Free State came to an end with the coming into force of a new constitution on 29 December 1937 when the state took the name 'Ireland'." [Wikipedia]