An island of the British Isles, lying west of Great Britain. Four-fifths of it is occupied by the Irish Republic (see ireland, republic of) and the remainder by Northern Ireland, which is part of the United Kingdom. Settled by the Celts, the country became divided into independent tribal territories over which the lords of Tara exercised nominal suzerainty. Christianity reached Ireland, probably in the 4th century, to be consolidated by the work of St Patrick, and after the breakup of the Roman Empire the country became for a time a leading cultural centre, with the monasteries fostering learning and missionary work. English invasions began in the 12th century under Henry II, but the authority that he established was never secure and by the 16th century was confined to an area around Dublin (the English Pale) until the Tudors succeeded in extending it over the whole of the island. Revolts against English rule, and against the imposition of Protestantism (which met with unexpectedly stubborn resistance), resulted in the plantation of Ireland by English (and later Scottish) families on confiscated land in an attempt to anglicize the country and secure its allegiance. In Ulster in particular the descendants of such settlers retained a distinctive identity. After an unsuccessful rebellion in 1798, political union of Britain and Ireland followed in 1801. In spite of genuine efforts towards its success Ireland sank deeper into destitution. A share of Britain’s industrial prosperity reached Protestant Ulster, but the rest of the island found its agricultural assets dropping in value. Unscrupulous absentee landlords undermined the ability of the local population to make a living and at the failure of the potato crop (Ireland’s staple) in the 1840s about a million people died in the famine, a million more fled abroad. The Home Rule movement, led by Parnell, failed to achieve its aims in the 19th century and implementation of a bill passed in 1914 was delayed by the outbreak of World War I. An armed uprising at Easter, 1916, was suppressed. Ireland was partitioned by the Anglo-Irish Treaty of 1921, which gave dominion status to Ireland with the exception of six of the counties of Ulster (Northern Ireland), whose Protestant majority wished to preserve the Union and which remained part of the United Kingdom.