Henry II and the Normans were the first group of people to colonize Ireland during the twelfth century. By the eighteenth the Ascendancy, which was made up of the Protestant elite landowners, had passed laws known as the Penal Laws that were meant to oppress the catholic population by excluding them from the legal bar, universities, the navy, and other parts of civil life.
The United Irishmen was the first group that pushed for Catholic emancipation during the eighteenth century. The United Irishmen were base on the principles of the French and wished to become its own republic free from Great Britain. One of the leaders was Theobald Wolfe Tone. (1763-98)
As a result of the uprisings Prime Minister William Pitt decided to abolish the Irish Parliament and push for a full union of Ireland with Great Britain. On January 1, 1801 the Act of Union became official uniting the two regions. There was very little popular support for this union, which did almost nothing to improve Irish political voice or correct the inequality in political representation. By 1874 there was a strong development of the Home Rule Party which was then in favor of breaking away from Great Britain and making Ireland an Independent state.
Many Catholic men started to join radical military groups such as The Irish Volunteers and The Irish Republican Brotherhood that were dedicated to the fight for Home Rule. The Irish Republican Brotherhood was responsible for the Easter Rising of 1916, in which they took control of multiple public buildings.
The leaders of The Irish Republican Brotherhood during the time of the rising, Padraic Pearse (1879-1916) and James Connolly (1864-1916), were executed for their actions. Eamon de Valera ( 1882- 1975 ) and Michael Collins ( 1890-1922) became the new leaders of the cause. Eamon de Valera was elected president of the left-wing republican party, Sinn Fein in 1916.
In 1918 as a protest of the Lloyd George legislation, the Irish delegates refused to take their seats in parliament and instead formed their own Republican parliament, called Dail Eireann. After years of fighting on December 6, 1921 the Anglo Irish Treaty was signed. The treaty created the Irish free State in the south, but allowed the six northern counties in Ulster to remain a part of the United Kingdom, as this region was mainly Protestant and in support of the Great Britain union. In 1949 Ireland became a republic no longer apart of the Empire.
The British Broadcasting Company website has more information about the Ireland and the creation of Northern Ireland and the troubles.
O'Brien, Máire, and Conor Cruise O'Brien. A Concise History of Ireland. New York, NY: Thames and Hudson, 1985.
Wasson, Ellis A. A History of Modern Britain: 1714 to the Present. Oxford: Wiley-Blackwell, 2010.