What little is known of pre-Christian Ireland comes from a few references in Roman writings, Irish poetry and myth, and archaeology. The earliest inhabitants--people of a mid-Stone Age culture--arrived about 6000 BC, when the climate had become hospitable following the retreat of the polar icecaps. About 4,000 years later, tribes from southern Europe arrived and established a high Neolithic culture, leaving behind gold ornaments and huge stone monuments for archaeologists. This culture apparently prospered, and the island became more densely populated. The Bronze Age people, who arrived during the next 1,000 years, produced elaborate gold and bronze ornaments and weapons.
The Iron Age arrived abruptly in the fourth century BC with the invasion of the Celts, a tall, energetic people who had spread across Europe and Great Britain in the preceding centuries. The Celts, or Gaels, and their more numerous predecessors divided into five kingdoms in which, despite constant strife, a rich culture flourished. This pagan society was dominated by druids--priests who served as educators, physicians, poets, diviners, and keepers of the laws and histories.
But the coming of Christianity from across the Irish Sea brought major changes and civilizing influences. Tradition maintains that in 432 AD, St. Patrick arrived on the island and, in the years that followed, worked to convert the Irish to Christianity. Probably a Celt himself, St. Patrick preserved the tribal and social patterns of the Irish, codifying their laws and changing only those that conflicted with Christian practices. He also introduced the Roman alphabet, which enabled Irish monks to preserve parts of the extensive Celtic oral literature.
The pagan druid tradition collapsed in the face of the spread of the new faith, and Irish scholars excelled in the study of Latin learning and Christian theology in the monasteries that shortly flourished. Missionaries from Ireland to England and the continent spread news of the flowering of learning, and scholars from other nations came to Irish monasteries. The excellence and isolation of these monasteries helped preserve Latin learning during the Dark Ages. The arts of manuscript illumination, metalworking, and sculpture flourished and produced such treasures as the Book of Kells, ornate jewelry, and the many carved stone crosses that dot the island.
This golden age of culture was interrupted by 200 years of intermittent warfare with waves of Viking raiders who plundered monasteries and towns. The Vikings established Dublin and other seacoast towns but were eventually defeated by the High King Brian Boru. Although the Irish were subsequently free from foreign invasion for 150 years, internecine clan warfare continued to drain their energies and resources.
In the 12th century, Pope Adrian IV, the only English Pope, granted overlordship, but not the requested absolute ownership, of the island to Henry II of England, who began an epic struggle between the Irish and the English which not only burned intermittently for 800 years but which continues to affect Irish politics and bilateral relations to this day. The Reformation exacerbated the oppression of the Roman Catholic Irish, and, in the early 17th century, Scottish and English Protestants were sent as colonists to the north of Ireland and the Pale around Dublin.
From 1800 to 1921, Ireland was an integral part of the United Kingdom. Religious freedom was restored in 1829. But this victory for the Irish Catholic majority was overshadowed by severe economic depression and mass famine from 1846-1848 when the potato crop failed and some 1.5 million people starved to death. The famine spawned the first mass wave of Irish emigration to the United States. A decade later, in 1858, the Irish Republican Brotherhood (IRB--also known as the Fenians) was founded as a secret society dedicated to armed rebellion against the British. An above-ground political counterpart, the Home Rule Movement, was created in 1874, advocating constitutional change for independence. Galvanized by the leadership of Charles Stewart Parnell, the party was able to force British governments after 1885 to introduce several home rule bills. The turn of the century witnessed a surge of interest in Irish nationalism, including the founding of Sinn Fein ("Ourselves Alone") as an open political movement.
Nationalism was and is a potent populist force in Irish politics. The outbreak of war in Europe in 1914 put home rule efforts on hold, and, in reaction, Padraic Pearse and James Connolly led the unsuccessful Easter Rising of 1916. The decision by the British-imposed court structure to execute the leaders of the rebellion, coupled with the British Government's threat of conscription, alienated public opinion and produced massive support for Sinn Fein in the 1918 general election. For several years the Irish Republican Army engaged in guerrilla warfare. Under the leadership of Eamon de Valera, the elected Sinn Fein deputies constituted themselves as the first Dail. Tensions only increased: British attempts to smash Sinn Fein ignited the Anglo-Irish War of 1919-1921.
The end of the war brought the Anglo-Irish treaty of 1921, which established the Irish Free State, or Éire, consisting of the 23 southern counties of Leinster, Munster and Connaught and three counties in Ulster (Cavan, Monaghan and Donegal). The treaty also recognized the partition of the island into Ireland and Northern Ireland, though supposedly as a temporary measure: the remaining six counties in Ulster (Antrim, Armagh, Derry, Down, Fermanagh and Tyrone) became Northern Ireland and remained part of the United Kingdom. The six predominantly Protestant counties of northeast Ulster--Northern Ireland--remained a part of the United Kingdom with limited self-government. A significant 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 (1922-1923), 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; however, it does not normally use the term "Republic of Ireland," which tacitly acknowledges the partition but refers to the country simply as "Ireland."
On April 18, 1949 the Irish Free State ceased to exist and Ireland formally became a republic, adopting the name Ireland or Eire, and withdrew from the British Commonwealth; it joined the European Community in 1973.
Irish governments have nominally sought the peaceful unification of Ireland and in recent decades have cooperated with Britain against terrorist groups such as the Provisional IRA and 'Real IRA' (see Irish Republican Army).