The formation of the United Kingdom of Great Britain and Northern Ireland has involved personal and political union across Great Britain and the wider British Isles. The United Kingdom is the most recent of a number of sovereign states that have been established in Great Britain at different periods in history, in different combinations and under a variety of polities. Historian Norman Davies has counted sixteen different states over the past 2,000 years.Davies, Norman. The Isles: A History. (London: Macmillan, 1999. ).

By the start of the 16th century, the number of states in Great Britain had been reduced to two: the Kingdom of England (which included Wales and controlled Ireland) and the Kingdom of Scotland. The once independent Principality of Wales fell under the control of English monarchs from the Statute of Rhuddlan in 1284. The Union of Crowns in 1603, the accidental consequence of a royal marriage one hundred years earlier, united the kingdoms in a personal union, though full political union in the form of the Kingdom of Great Britain required a Treaty of Union in 1706 and Acts of Union in 1707 (to ratify the Treaty).

The Acts of Union 1800 united the Kingdom of Great Britain with the Kingdom of Ireland, which had been gradually brought under English control between 1541 and 1691, to form the United Kingdom of Great Britain and Ireland in 1801. Independence for the Irish Free State in 1922 followed the partition of the island of Ireland two years previously, with six of the nine counties of the province of Ulster remaining within the UK, which then changed to the current name in 1927 of the United Kingdom of Great Britain and Northern Ireland.

In the 20th century, the rise of Welsh and Scottish nationalism and resolution of the Troubles in Ireland resulted in the establishment of devolved parliaments or assemblies for Northern Ireland, Scotland and Wales. Although separatism has increased in support since devolution was introduced.

Background

England's conquest of Wales

Through internal struggles and dynastic marriage alliances, the Welsh became more united until Owain Gwynedd (1100–1170) became the first Welsh ruler to use the title princeps Wallensium (prince of the Welsh). After invading England, land-hungry Normans started pushing into the relatively weak Welsh Marches, setting up a number of lordships in the eastern part of the country and the border areas. In response, the usually fractious Welsh, who still retained control of the north and west of Wales, started to unite around leaders such as Owain Gwynedd's grandson Llywelyn the Great (1173–1240), who is known to have described himself as "prince of all North Wales".p.239, Davies, R. R. 1987. Conquest, coexistence and change: Wales 1063–1415 Clarendon Press, University of Wales Press. Llywelyn wrestled concessions out of Magna Carta in 1215 and received the fealty of other Welsh lords in 1216 at the council at Aberdyfi, becoming the first Prince of Wales. His grandson, Llywelyn ap Gruffudd, also secured the recognition of the title Prince of Wales from Henry III with the Treaty of Montgomery in 1267. However, a succession of disputes, including the imprisonment of Llywelyn's wife Eleanor, daughter of Simon de Montfort, culminated in the first invasion by Edward I. Following a military defeat, the Treaty of Aberconwy in 1277 reasserted Llywelyn's fealty to the King of England.

In 1282, following another rebellion, Edward I finally made a permanent conquest. With Llywelyn dead, the King took over his lands and dispossessed various other allied princes of northern and western Wales,Michael Prestwich, Edward I (London: Methuen, 1988, updated edition Yale University Press, 1997 ) and across that area Edward established the counties of Anglesey, Caernarfonshire, Flintshire, Merionethshire, Cardiganshire and Carmarthenshire. The Statute of Rhuddlan formally established Edward's rule over Wales two years later although Welsh law continued to be used. Remaining princes became marcher lords. Edward's son (later Edward II), who had been born in Wales, was made Prince of Wales. The tradition of bestowing the title "Prince of Wales" on the heir of the British Monarch continues to the present day. To help maintain his dominance, Edward constructed a series of great stone castles.

Initially, the Crown had only indirect control over much of Wales because the marcher lords (ruling over independent lordships in most of the country) were independent from direct Crown control. The exception was the lands of the Principality of Wales in the north and west of the country, which was held personally by the King (or the heir to the Crown) but was not incorporated into the Kingdom of England. However, between the 13th and 16th centuries the Crown gradually acquired most of the marcher lordships, usually through inheritance, until almost all of Wales came under Crown control. Nevertheless, the whole of Wales – that is, the Principality, marcher lordships held by the Crown and marcher lordships held by others – remained outside of the legal and constitutional structures of the Kingdom of England.

There was no major uprising except that led by Owain Glyndŵr a century later, against Henry IV of England. In 1404 Glyndŵr was crowned Prince of Wales in the presence of emissaries from France, Spain, and Scotland; he went on to hold parliamentary assemblies at several Welsh towns, including Machynlleth. The rebellion was ultimately to founder, however. Glyndŵr went into hiding in 1412, and peace was more or less restored in Wales by 1415.

The power of the marcher lords was ended in 1535, when the political and administrative union of England and Wales was completed. The Laws in Wales Act 1535 annexed Wales to England and extended English law to Wales, abolished the marcher lordships and partitioned their lands into the counties of Brecon, Denbigh, Monmouth, Montgomery, and Radnor while adding parts to Gloucester, Hereford, and Salop. (Monmouthshire was wholly subsumed into the court structure of England and so omitted from the subsequent Laws in Wales Act 1542, which led to ambiguity about its status as part of England or Wales.) The Act also extended the Law of England to both England and Wales and made English the only permissible language for official purposes. This had the effect of creating an English-speaking ruling class amongst the Welsh, at a time when Welsh was the language of the great majority. Wales was also now represented in Parliament at Westminster.

English Conquest of Ireland

By the 12th century, Ireland was divided. Power was exercised by the heads of a few regional dynasties vying with each other for supremacy over the whole island. In 1155 Pope Adrian IV issued the papal bull Laudabiliter giving the Norman King Henry II of England lordship over Ireland. The bull granted Henry the right to invade Ireland in order to reform Church practices. When the King of Leinster Diarmuid MacMorroug was forcibly exiled from his kingdom by the new High King, Ruaidri mac Tairrdelbach Ua Conchobair, he obtained permission from Henry II of England to use Norman forces to regain his kingdom. The Normans landed in Ireland in 1169, and within a short time Leinster was reclaimed by Diarmait, who named his son-in-law, Richard de Clare, heir to his kingdom. This caused consternation to Henry, who feared the establishment of a rival Norman state in Ireland.

With the authority of the papal bull Henry landed with a large fleet in 1171 and claimed sovereignty over the island. A peace treaty followed in 1175, with the Irish High King keeping lands outside Leinster, which had passed to Henry on the expected death of both Diarmait and de Clare. When the High King lost his authority Henry awarded his Irish territories to his younger son John with the title Dominus Hiberniae ("Lord of Ireland") in 1185. When John unexpectedly became King of England, the Lordship of Ireland fell directly under the English Crown. The title of Lord of Ireland and King of England fell into personal union. Throughout the 13th century the policy of the English Kings was to weaken the power of the Norman Lords in Ireland.

There was a resurgence of Gaelic power as rebellious attacks stretched Norman resources. Politics and events in Gaelic Ireland also served to draw the settlers deeper into the orbit of the Irish. When the Black Death arrived in Ireland in 1348 it hit the English and Norman inhabitants who lived in towns and villages far harder than it did the native Irish, who lived in more dispersed rural settlements. After it had passed, Gaelic Irish language and customs came to dominate the countryside again. The English-controlled area shrunk back to the Pale, a fortified area around Dublin.

Outside the Pale, the Hiberno-Norman lords adopted the Irish language and customs. Over the following centuries they sided with the indigenous Irish in political and military conflicts with England and generally stayed Catholic after the Reformation. The authorities in the Pale grew so worried about the "Gaelicisation" of Ireland that they passed special legislation banning those of English descent from speaking the Irish language, wearing Irish clothes, or inter-marrying with the Irish. Since the government in Dublin had little real authority, however, the Statutes did not have much effect. By the end of the 15th century, the ruling English authority in Ireland had almost all disappeared.

In 1532, Henry VIII broke with Papal authority. While the English, the Welsh, and the Scots accepted Protestantism, the Irish remained Catholic. This affected Ireland's relationship with England for the next four hundred years since the English tried to re-conquer and colonise Ireland to prevent Ireland being a base for Catholic forces that were trying to overthrow the Protestant settlement in England.

From 1536, Henry VIII decided to conquer Ireland and bring it under crown control so the island would not become a base for future rebellions or foreign invasions of England. In 1541, he upgraded Ireland from a lordship to a full kingdom. Henry was proclaimed King of Ireland at a meeting of the Irish Parliament. With the institutions of government in place, the next step was to extend the control of the English Kingdom of Ireland over all of its claimed territory. The re-conquest was completed during the reigns of Elizabeth and James I, after several bloody conflicts. However, the English were not successful in converting the Catholic Irish to the Protestant religion, and the brutal methods used by Crown authority to pacify the country heightened resentment of English rule.

From the mid-16th and into the early 17th century, Crown governments carried out a policy of colonisation known as Plantations. Scottish and English Protestants were sent as colonists to the provinces of Munster, Ulster, and the counties of Laois and Offaly. These settlers, who had a British Protestant identity, would form the ruling class of future British administrations in Ireland. A series of Penal Laws discriminated against all faiths other than the established (Anglican) Church of Ireland.

Personal Union: Union of the Crowns

In August 1503 James IV, King of Scots, married Margaret Tudor, the eldest daughter of Henry VII of England. Almost 100 years later, when Elizabeth I was in the last decade of her reign, it was clear to all that James VI of Scotland, the great-grandson of James IV and Margaret Tudor, was the only generally acceptable heir to the English throne. From 1601, Elizabeth I's chief minister Sir Robert Cecil maintained a secret correspondence with James in order to prepare in advance for a smooth succession. Elizabeth died on 24 March 1603, and James was proclaimed king in London later the same day. Despite sharing a monarchy, Scotland and England continued as separate countries with separate parliaments for over one hundred more years.