Originally Posted by Wikipedia
Empire Day was introduced in the UK in 1904 by the 7th Earl of Meath, 'to nurture a sense of collective identity and imperial responsibility among young empire citizens'. In schools, morning lessons were devoted to "exercises calculated to remind (the children) of their mighty heritage". The centrepiece of the day was an organised and ritualistic veneration of the Union flag. Then, schoolchildren were given the afternoon off, and further events were usually held in their local community.
Empire Day became more of a sombre commemoration in the aftermath of World War I, and politically partisan as the Labour Party passed a resolution in 1926 to prevent the further celebration of Empire Day. After World War II, the event fell into rapid decline, and Prime Minister Harold Macmillan bowed to the inevitable on 18 December 1958, when he announced in Parliament that the name of Empire Day would be changed forthwith to Commonwealth Day.