England and Scotland merged politically in 1707 after the crowns of both counties were united in 1603, but the crown of Ireland did not merge with the Union until 1800. Part of the attraction of the Union for many Irish Catholics was the promise of Catholic Emancipation, allowing Roman Catholic MPs, who had not been allowed in the Irish Parliament. This was however blocked by King George III who argued that emancipating Roman Catholics would breach his Coronation Oath, and was not realised until 1829.