From 1801 to 1921, all of Ireland was part of the same country, called the United Kingdom of Great Britain and Ireland. In 1919, a war broke out, the Irish War of Independence, and on December 6 1921, the Irish Free State became independent. After a new constitution came into effect in 1937, the state became a republic. Northern Ireland stayed with the UK, and this would lead to The Troubles beginning in the 1960s and ending with the Good Friday Agreement signed in 1998.