 The earliest evidence of human presence in Ireland is dated at 10 @,@ 500 BC . Gaelic Ireland had emerged by the 1st century AD and lasted until the First World War . The island was <unk> from the 5th century onward . Following the Norman invasion in the 12th century , England claimed sovereignty over Ireland . However , English rule did not extend over the whole island until the 16th – 17th century Tudor conquest , which led to colonisation by settlers from Britain . In the <unk> , a system of Protestant English rule was designed to materially disadvantage the Catholic majority and Protestant dissenters , and was extended during the 18th century . With the Acts of Union in 1801 , Ireland became a part of the United Kingdom . A war of independence in the early 20th century was followed by the partition of the island , creating the Irish Free State , which became increasingly sovereign over the following decades , and Northern Ireland , which remained a part of the United Kingdom . Northern Ireland saw much civil unrest from the late 1960s until the 1990s . This subsided following a political agreement in 1998 . In 1973 the Republic of Ireland joined the European Economic Community while the United Kingdom , and Northern Ireland , as part of it , did the same . 
