Beginning in the 16th century, the British Isles underwent a series of political changes that eventually led to the establishment of the United Kingdom of Great Britain and Ireland in 1801. The creation of the United Kingdom brought England, Scotland, Ireland, and Wales (the four cultural regions of Britain) under the rule of a central government headed by a common monarch and administered by a single parliament. When Ireland (with the exception of its six northern counties) achieved independence in 1922, the kingdom was renamed the United Kingdom of Great Britain and Northern Ireland.
England and Wales were the first regions to function under a single government. During the 13th century, England established control over Wales after several centuries of intermittent warfare. The two nations officially merged in 1536 and were known collectively as England.
Scotland and England moved toward union after the Scottish monarchs inherited the throne of England in 1603. Although a common ruler united these two countries, Scotland and England remained separate nations with separate governments. In 1707 the Scottish and English parliaments passed an Act of Union, which merged the formerly independent nations into the Kingdom of Great Britain.
The English established control over Ireland beginning in the 12th century, when English colonists invaded the island. They gradually established English domination over the entire island. Ireland remained a separate country under the rule of the English and British monarchs until the British Parliament passed the Act of Union of 1800. This act created the United Kingdom of Great Britain and Ireland.
However, opposition to the United Kingdom remained strong among Ireland's predominantly Roman Catholic population. Many Irish citizens resented the long history of domination by Britain's Protestant majority. In 1922 Ireland achieved its independence, although its six northern counties, where Protestants are in the majority, remained a part of the United Kingdom.
For a history of the nations of Britain prior to 1707, see Scotland; Britain, Ancient; England; and Wales. For a history of Ireland prior to 1800, see Ireland.