The Irish Free State was established by a treaty with Great Britain that went into effect in 1922. Signing the treaty for Ireland were Michael Collins and Arthur Griffith, leaders of Sinn Fein, the group that had led the war for independence. Griffith became head of a provisional government. A third leader, Eamon de Valera, objected to the new state being a dominion of the British Empire. A civil war between de Valera's Republicans and the Free-Staters lasted a year and was won by the Free-Staters. The new government was installed in 1922, with William Cosgrave president of the executive council (cabinet).

De Valera formed a new party, the Fianna Fáil (Soldiers of Destiny), whose candidates ran in the election of 1927. By 1932 the party had become strong enough to get de Valera elected president of the executive council. In 1937 a new constitution, adopting “Eire” (Gaelic for “Ireland”) as the name of the country and declaring it sovereign and independent, went into effect. Douglas Hyde was elected president. De Valera became prime minister.

In World War II, Ireland remained neutral. It withdrew from the British Commonwealth and was declared a republic in 1949. De Valera served as its first president.

From 1956 to 1962, the outlawed Irish Republican Army waged a terrorist campaign against Northern Ireland to end by force the partition of Ireland. Although reunion has been a major goal of the Irish Republic, it has not attempted to force the issue. However, when civil strife between Catholics and Protestants in Northern Ireland began in 1969, there was open support for the Catholic minority. Soon the terrorist tactics of the Irish Republican Army (IRA), outlawed since 1936, caused a change of attitude, both popular and governmental. Stern measures were taken against the IRA in Ireland.

In a referendum in 1973, a provision of the constitution that made Roman Catholicism the official religion was repealed. Also in that year Ireland became a member of what is now the European Union. In 1990 Mary Robinson was elected president—the first woman in Irish history to hold that office. A 1995 referendum overturned the country's constitutional ban on divorce.

As part of the Anglo-Irish Agreement reached with Britain in 1985, Ireland participated in discussions over the future of Northern Ireland. In the mid-1990's Republican and Unionist groups from the North joined the negotiations after announcing cessation of their terrorist campaigns. In 1998 the parties signed an agreement establishing the Northern Ireland Assembly and ending direct rule from London.

Important dates in Ireland
c. 400 B.C. Celtic tribes invaded Ireland.
A.D. 432 Saint Patrick brought Christianity to Ireland.
c. 550 The age of Irish monasteries (religious centers) began.
c. 795 Vikings began raiding.
1014 Brian Boru defeated the Vikings at Clontarf.
1106 Turlough O'Connor became king of Connacht.
1169 A party of Normans led by Robert FitzStephen landed on the southeast coast of Ireland and began to seize territories.
1171 King Henry II arrived from England and took control of most Irish kingdoms.
1494 Lord deputy Edward Poyning summoned a parliament in Dublin that passed laws giving the kings of England control of the lawmaking in Ireland.
1541 King Henry VIII of England was declared king of Ireland by an Irish Parliament dominated by nobles who favored English rule.
1580 Queen Elizabeth began the plantation of Munster, taking land from Irish owners and giving it to English colonists.
1594-1603 Irish rebels led by Hugh O'Neill of Tyrone and Red Hugh O'Donnell of Tyrconnell led a series of revolts that ended with a failed invasion by Spanish forces and the defeat of O'Neill and O'Donnell.
1607 The earls of Tyrone and Tyrconnell fled Ireland, and James I began the plantation of Ulster.
1649 Oliver Cromwell crushed an Irish revolt against England with massacres of the garrisons at Drogheda and Wexford and took land and political rights away from Irish Catholics.
1690 The English defeated James II and Irish forces in the Battle of the Boyne.
1695-1728 The British government passed the Penal Laws, a series of harsh religious laws against the Irish Roman Catholics.
1798 A French force landed in County Mayo and staged a brief rebellion near Castlebar. The British brutally suppressed the rebellion, killing or wounding thousands.
1801 Ireland became part of the United Kingdom of Great Britain and Ireland.
1845-1848 A potato blight and the starvation and disease that followed killed about 1 million people.
1870 Isaac Butt, a Protestant lawyer, founded the home rule movement, calling for Ireland to be given its own parliament in Dublin to deal with Irish affairs.
1916 The Easter Rising against British rule erupted in Dublin.
1921 Ireland became a dominion of the British Commonwealth called the Irish Free State.
1949 Ireland declared itself a republic.
1985 Ireland was given an advisory role—but no direct powers—in Northern Ireland's government.
1999 Ireland began taking part in new governing bodies created by the Northern Ireland peace agreement.