The Republic of Ireland had no relations with Northern Ireland for most of the twentieth century.
Ireland . 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 . Republic of Ireland . The state shares its only land border with Northern Ireland , a part of the United Kingdom . The state had no formal relations with Northern Ireland for most of the twentieth century , but during the 1980s and 1990s the British and Irish governments worked with the Northern Ireland parties towards a resolution to `` the Troubles '' .