The former kingdoms had shared the same monarch since James VI , King of Scots , became King of England in 1603 following the death of Queen Elizabeth I , bringing about a `` Union of the Crowns '' .
The two earlier kingdoms of Scotland and England had been in a personal union , sharing the same head of state since James VI , King of Scots , became King of England in 1603 following the death of Queen Elizabeth I . In 1801 , by the Act of Union 1800 , the Kingdom of Great Britain and the Kingdom of Ireland were joined together into the United Kingdom of Great Britain and Ireland after the putting down of the Irish Rebellion of 1798 .