England and Wales, 1536: King Henry VIII Tudor, united England and Wales under one Parliament in 1536
Scotland, 1603 - 1707: In Scotland a similar thing happened. Elizabeth I of England (and Wales) had left no heir. So James, son of her cousin Mary, Queen of Scots, inherited the crown becoming King James I of England and Wales and King James VI of Scotland in 1603. The Parliaments of England and Wales and Scotland were united a century later in 1707
Ireland, 1801: The whole of Ireland was united with Great Britain from 1801 up until 1922. In that year the independent Republic of Ireland was formed in the South, while Northern Ireland remained part of the United Kingdom of Great Britain and Northern Ireland
