The Irish people are mainly of Celtic origin, with the nation's only remarkable sized minority having descended from the Anglo-Normans. English is the common language, but Irish also is an official language and is taught in the schools.

The end of the war brought the Anglo-Irish treaty of 1921, which accomplished the Irish Free State of 26 counties within the British Commonwealth and recognized the partition of the island into Ireland and Northern Ireland, though supposedly as a temporary measure. The six predominantly Protestant counties of northeast Ulster-Northern Ireland-remained a part of the United Kingdom with limited self-government. A remarkable Irish minority repudiated the treaty settlement because of the continuance of subordinate ties to the British monarch and the partition of the island. This opposition led to further hostilities-a civil war (1922-23), which was won by the pro-treaty forces. In 1932, Eamon de Valera, the political leader of the forces initially opposed to the treaty, became prime minister, and a new Irish constitution was enacted in 1937. The last British military bases were soon withdrawn, and the ports were returned to Irish control. Ireland was neutral in World War II. The government formally declared Ireland a republic in 1948; it does not normally use the term "Republic of Ireland," which tacitly acknowledges the partition but refers to the nation simply as "Ireland."