Since the Acts of Union of 1707

Main article: History of the United Kingdom

The Treaty of Union led to a single united kingdom encompassing all Great Britain.

On 1 May 1707, a new kingdom of Great Britain came into being, created by the political union of the kingdoms of England and Scotland in accordance with the Treaty of Union that had been negotiated the previous year and ratified by the English and Scottish Parliaments passing Acts of Union.

In the 18th century, the country played an important role in developing Western ideas of the parliamentary system as well as making significant contributions to literature, the arts, and science. The British-led Industrial Revolution transformed the country and fuelled the growing British Empire. During this time Britain, like other great powers, was involved in colonial exploitation, including the Atlantic slave trade, although with the passing of the Slave Trade Act of 1807 the United Kingdom took a leading role in battling the trade in slaves. The colonies in North America had been the main focus of British colonial activity. However, with their loss following the American War of Independence, imperial ambition turned to other parts of the globe, particularly India.

In 1800, while the wars with France still raged, the Parliaments of Great Britain and of Ireland each passed an Act of Union, uniting the two kingdoms and creating the United Kingdom of Great Britain and Ireland, which came into being on 1 January 1801.

The Battle of Waterloo marked the end of theNapoleonic Wars and the start of Pax Britannica.

After the defeat of France in the Revolutionary and Napoleonic Wars (1792–1815), the United Kingdom emerged as the principal naval and economic power of the 19th century (with London the largest city in the world from about 1830 to 1930) and remained a foremost power into the mid-20th century. Unchallenged at sea, Britain adopted the role of global policeman, a state of affairs later known as the Pax Britannica. It was also a period of rapid economic, colonial, and industrial growth. Britain was described as the "workshop of the world", and the British Empire grew to include India, largeparts of Africa, and many other territories across the world. Alongside the formal control it exerted over its own colonies, Britain's dominant position in world trade meant that it effectively controlled the economies of many countries, such as China, Argentina and Siam. Domestically, there was a shift to free trade and laissez-faire policies and a very significant widening of the voting franchise. The country saw a huge population increase during the century, accompanied by rapid urbanization, resulting in significant social and economic stresses. By the end of the century, other states began to challenge Britain's industrial dominance.

Infantry of the Royal Irish Rifles during the Battle of the Somme. More than 885,000 British soldiers lost their lives on the battlefields of World War I.

The UK, along with Russia, France and (after 1917) the USA, was one of the major powers opposing the German Empire and its allies in World War I (1914–18). The UK armed forces grew to over five million people engaged across much of its empire and several regions of Europe, and increasingly took a major role on the Western front. The nation suffered an estimated two and a half million casualties and finished the war with a huge national debt. After the war the United Kingdom received the League of Nations mandate over former German and Ottoman colonies, and the British Empire had expanded to its greatest extent, covering a fifth of the world's land surface and a quarter of its population. However, the rise of Irish Nationalism and disputes within Ireland over the terms of Irish Home Rule led eventually to the partition of the island in 1921, with the Irish Free State becoming independent with Dominion statusin 1922, and Northern Ireland remaining part of the United Kingdom. The Great Depression (1929–32) occurred at a time when the UK was still far from having recovered from the effects of the war, and led to hardship as well as political and social unrest.

The United Kingdom was one of the Allies of World War II and an original signatory to the Declaration of the United Nations. Following the defeat of its European allies in the first year of the war, the United Kingdom continued the fight against Germany, notably in the Battle of Britain and the Battle of the Atlantic. After the victory, the UK was one of the Big Three powers that met to plan the post-war world. The war left the United Kingdom financially damaged. However, Marshall Aid and loans from both the United States and Canada helped the UK on the road to recovery.

Territories that were at one time part of theBritish Empire. Current British Overseas Territoriesare underlined in red.

The Labour government in the immediate post-war years initiated a radical programme of changes having a significant impact on British society for the following decades. Domestically, major industries and public utilities were nationalized, a Welfare Statewas established, and a comprehensive publicly funded healthcare system, the National Health Service, was created. In response to the rise of local nationalism, the Labour government's own ideological sympathies and Britain's now diminished economic position, a policy of decolonisation was initiated with the granting of independence to India and Pakistan in 1947. Over the next three decades most territories of the Empire gained independence and became sovereign members of the Commonwealth of Nations.

Although the new post-war limits of Britain's political role were illustrated by the Suez Crisis of 1956, the UK nevertheless became one of the five permanent members of the United Nations Security Council and was the third country to develop a nuclear weapons arsenal (with its first atomic bomb test in 1952). The international spread of the English language also ensured the continuing international influence of its literature and culture, while from the 1960s its popular culture also found influence abroad. As a result of a shortage of workers in the 1950s, the British Government encouraged immigration from Commonwealth countries, thereby transforming Britain into a multi-ethnic society in the following decades. In 1973, the United Kingdom joined the European Economic Community (EEC), and when the EEC became the European Union (EU) in 1992, the UK was one of its 12 founding members. From the late 1960s Northern Ireland suffered communal and paramilitary violence (sometimes affecting elsewhere in the UK and also the Republic of Ireland) conventionally known as the Troubles. It is usually considered to have ended with the Belfast "Good Friday" Agreement of 1998.

Following a period of global economic slowdown and industrial strife in the 1970s, the Conservative Government of the 1980s initiated a radical policy of deregulation, particularly of the financial sector, flexible labour markets, the sale of state-owned companies (privatisation), and the withdrawal of subsidies to others. Aided, from 1984, by the inflow of substantial North Sea oil revenues, the UK experienced a period of significant economic growth. Around the end of the 20th century there were major changes to the governance of the UK with the establishment of devolved national administrations for Northern Ireland, Scotland, and Wales following pre-legislative referendums, and the statutory incorporation of the European Convention on Human Rights. Domestic controversy surrounded some of Britain's overseas military deployments in the 2000s (decade), particularly in Iraq and Afghanistan.