The roots of the conflict in Northern Ireland go back to the early 17th Century, when English and Scottish settlers were encouraged through the provision of confiscated land to colonize Ireland. Subsequent centuries of such colonization -- often verey heavy-handed colonization -- by the Protestant Crown of England of Catholic Ireland would become a festering would not just for Great Britain but for the United States for many years.
For 300 years, a series of militant and political movements inside Ireland railed and fought against Enlish domination. The 1801 incorporation of Ireland into the United Kingdom both cemented the Crown's hold on its colony and inflamed Irish nationalists. Following the Irish War of Independence in 1919, during which the nationalists, now referred to as republicans, increased pressure for independence from Great Britain. The partition or Ireland into a northern province of Great Britain, dominated by Protestants, and a Catholic-dominated Republic of Ireland to the south was established with the Government of Ireland Act of 1920.
While the Irish War of Independence did not result in a unified Ireland free of British rule, it did result in the signing of the Anglo-Irish Treaty, which ostensibly created a unified nation, but in name only. The Irish Free State, as it was called, constituted the whole of the island, but pro-Britain Protestants continued to fight both politically and militarily for unification with England, which effectively occurred in 1922.
For the remainder of the century, Catholics in Northern Ireland agitated for independence. The protracted period known as The Troubles, beginning in the late 1960s and ending officially with the 1998 signing of the Good Friday Agreement, saw terrible violence between the Irish Republican Army and its offshoots on one side and the British Army and Protestant militias on the other. One of the more infamous incidences of this period was Bloody Sunday, when, on January 30,1972, British soldiers opened fire on demonstrating Catholics, killing 14.
The conflict was finally resolved when the U.S. brokered a peace agreement known as the Good Friday Agreement of April 1998. During this entire conflict, the United Nations was, for all practical purposes, a nonentity. With Great Britain being a permanent member of the U.N. Security Council and, consequently, having a veto over binding resolutions, and with IRA terrorists killing indiscriminately, there was nothing the U.N. was able to do.