The United Kingdom has historically played a leading role in developing parliamentary democracy and in advancing literature and science. At its zenith in the 19th century, the British Empire stretched over one-fourth of the earth's surface. The first half of the 20th century saw the UK's strength seriously depleted in two world wars and the Irish Republic's withdrawal from the union. The second half witnessed the dismantling of the Empire and the UK rebuilding itself into a modern and prosperous European nation. As one of five permanent members of the UN Security Council and a founding member of NATO and the Commonwealth, the UK pursues a global approach to foreign policy. The UK is also an active member of the EU, although it chose to remain outside the Economic and Monetary Union. The Scottish Parliament, the National Assembly for Wales, and the Northern Ireland Assembly were established in 1999. The latter was suspended until May 2007 due to wrangling over the peace process, but devolution was fully completed in March 2010.
The history of the United Kingdom as a unified sovereign state began in 1707 with the political union of the kingdoms of England and Scotland, into a united kingdom called Great Britain. On this new state the historian Simon Schama said "What began as a hostile merger would end in a full partnership in the most powerful going concern in the world... it was one of the most astonishing transformations in European history." A further Act of Union in 1800 added the Kingdom of Ireland to create the United Kingdom of Great Britain and Ireland.
The early years of the unified kingdom of Great Britain were marked by Jacobite risings which ended with defeat for the Stuart cause at Culloden in 1746. Later, in 1763, victory in the Seven Years War led to the dominance of the British Empire, which was to be the foremost global power for over a century and grew to become the largest empire in history. As a result, the culture of the United Kingdom, and its industrial, political, constitutional, educational and linguistic legacy, is widespread.
In 1922, following the Anglo-Irish Treaty, Ireland effectively seceded from the United Kingdom to become the Irish Free State; a day later, Northern Ireland seceded from the Free State and became part of the United Kingdom. As a result, in 1927 the United Kingdom changed its formal title to the "United Kingdom of Great Britain and Northern Ireland,"usually shortened to the "United Kingdom", the "UK" or "Britain". Former parts of the British Empire became independent dominions.
In the Second World War, in which the Soviet Union and the US joined Britain as allied powers, Britain and its Empire fought a successful war against Germany, Italy and Japan. The cost was high and Britain no longer had the wealth or the inclination to maintain an empire, so it granted independence to most of the Empire. The new states typically joined the Commonwealth of Nations. The United Kingdom has sought to be a leading member of the United Nations, the European Union and NATO, yet since the 1990s large-scale devolution movements in Northern Ireland, Scotland and Wales have brought into question the future viability of this constantly evolving political union.