On 1 May 1707, the Kingdom of Great Britain^[24][25] was created by the political union of the Kingdom of England (which included Wales) and the Kingdom of Scotland. This event was the result of the Treaty of Union that was agreed on 22 July 1706,^[26] and then ratified by both the Parliament of England and Parliament of Scotland each passing an Act of Union in 1707. Almost a century later, the Kingdom of Ireland, already under English control by 1691, joined the Kingdom of Great Britain with the passing of the Act of Union 1800.^[27] Although England and Scotland had been separate states prior to 1707, they had been in personal union since the Union of the Crowns in 1603, when James VI King of Scots had inherited the throne of the Kingdoms of England and Ireland and moved his court from Edinburgh to London.

In its first century, the United Kingdom played an important role in developing Western ideas of the parliamentary system as well as making significant contributions to literature, the arts, and science.^[30] The UK-led Industrial Revolution transformed the country and fuelled the growing British Empire. During this time, like other great powers, the UK was involved in colonial exploitation, including the Atlantic slave trade, although the passing of the Slave Trade Act in 1807 made it the first country to prohibit trade in slaves.^[31]

After the defeat of Napoleon in the Napoleonic Wars, the UK emerged as the principal naval power of the 19th century and remained an eminent power into the mid-20th century. The British Empire expanded to its maximum size by 1921, gaining the League of Nations mandate over former German and Ottoman colonies after World War I. One year later, the BBC, the world's first large-scale international broadcasting network, was created.

Long simmering tensions in Ireland led to the partition of the island in 1920, followed by independence for the Irish Free State in 1922 with Northern Ireland remaining within the UK. As a result, in 1927, the formal name of the UK was changed to its current name, the United Kingdom of Great Britain and Northern Ireland.

The UK fought Nazi Germany as one of the major Allied powers of World War II. At one stage in 1940, amid the Battle of Britain, it stood alone against the Axis. After the victory, the UK played a key role in designing a new world order. World War II left the United Kingdom financially damaged. However, Marshall Aid and costly loans taken from both Canada and the United States helped the UK on the road to recovery.

The immediate post-war years saw the establishment of the Welfare State, including among the world's first and most comprehensive public health services, while the demands of a recovering economy attracted immigrants from all over the Commonwealth. Although the new postwar limits of Britain's political role were confirmed by the Suez Crisis of 1956, the international spread of the English language meant the continuing influence of its literature and culture, while from the 1960s its popular culture also found influence abroad.

Following a period of global economic slowdown and industrial strife in the 1970s, the 1980s saw the inflow of substantial North Sea oil revenues and economic growth. The premiership of Margaret Thatcher marked a significant change of direction from the post-war political and economic consensus; a path that has continued under the New Labour governments of Tony Blair and Gordon Brown since 1997.

The United Kingdom was one of the 12 founding members of the European Union at its launch in 1992 with the signing of the Maastricht Treaty. Prior to that, it had been a member of the EU's forerunner, the European Economic Community (EEC), from 1973. The attitude of the present Labour government towards further integration with this organisation is mixed,with the Official Opposition, the Conservative Party, favouring less powers and competencies being transferred to the EU.

The end of the 20th century saw major changes to the governance of the UK with the establishment of devolved national administrations for Northern Ireland, Scotland, and Wales following pre-legislative referenda.

The Battle of Waterloo marked the end of the Napoleonic Wars.