United Kingdom of Great Britain and Ireland (1800)

Events that culminated in the union with Ireland had spanned several centuries. Invasions from England by the ruling Normans from 1170 led to centuries of strife in Ireland and successive Kings of England sought both to conquer and pillage Ireland, imposing their rule by force throughout the entire island. In the early 17th century, large-scale settlement by Protestant settlers from both Scotland and England began, especially in the province of Ulster, seeing the displacement of many of the native Roman Catholic Irish inhabitants of this part of Ireland. Since the time of the first Norman invaders from England, Ireland has been subject to control and regulation, firstly by England then latterly by Great Britain.

After the Irish Rebellion of 1641, Irish Roman Catholics were barred from voting or attending the Irish Parliament. The new English Protestant ruling class was known as the Protestant Ascendancy. Towards the end of the 18th century the entirely Protestant Irish Parliament attained a greater degree of independence from the British Parliament than it had previously held. Under the Penal Laws no Irish Catholic could sit in the Parliament of Ireland, even though some 90% of Ireland's population was native Irish Catholic when the first of these bans was introduced in 1691. This ban was followed by others in 1703 and 1709 as part of a comprehensive system disadvantaging the Catholic community, and to a lesser extent Protestant dissenters. In 1798, many members of this dissenter tradition made common cause with Catholics in a rebellion inspired and led by the Society of United Irishmen. It was staged with the aim of creating a fully independent Ireland as a state with a republican constitution. Despite assistance from France the Irish Rebellion of 1798 was put down by British forces.

Possibly influenced by the War of American Independence (1775–1783) , a united force of Irish volunteers used their influence to campaign for greater independence for the Irish Parliament. This was granted in 1782, giving free trade and legislative independence to Ireland. However, the French revolution had encouraged the increasing calls for moderate constitutional reform. The Society of United Irishmen, made up of Presbyterians from Belfast and both Anglicans and Catholics in Dublin, campaigned for an end to British domination. Their leader Theobald Wolfe Tone (1763–98) worked with the Catholic Convention of 1792 which demanded an end to the penal laws. Failing to win the support of the British government, he travelled to Paris, encouraging a number of French naval forces to land in Ireland to help with the planned insurrections. These were slaughtered by government forces, but these rebellions convinced the British under Prime Minister William Pitt that the only solution was to end Irish independence once and for all.

Henry Gratton, an Irish politician who opposed the union with Britain

The legislative union of Great Britain and Ireland was brought about by the Act of Union 1800, creating the "United Kingdom of Great Britain and Ireland". The Act was passed in both the Parliament of Great Britain and the Parliament of Ireland, dominated by the Protestant Ascendancy and lacking representation of the country's Roman Catholic population. Substantial majorities were achieved, and according to contemporary documents this was assisted by bribery in the form of the awarding of peerages and honours to opponents to gain their votes. Under the terms of the merger, the separate Parliaments of Great Britain and Ireland were abolished, and replaced by a united Parliament of the United Kingdom. Ireland thus became an integral part of the United Kingdom, sending around 100 MPs to the House of Commons at Westminster and 28 representative peers to the House of Lords, elected from among their number by the Irish peers themselves, except that Roman Catholic peers were not permitted to take their seats in the Lords. Part of the trade-off for the Irish Catholics was to be the granting of Catholic Emancipation, which had been fiercely resisted by the all-Anglican Irish Parliament. However, this was blocked by King George III, who argued that emancipating the Roman Catholics would breach his Coronation Oath. The Roman Catholic hierarchy had endorsed the Union. However the decision to block Catholic Emancipation fatally undermined the appeal of the Union.