 The term Jackeen is believed to be derived from the name Jack, a common English nickname for the names James and John, or in reference to the Union Jack, the flag of the United Kingdom.Following the Norman invasion of Ireland beginning in 1169, Dublin became the centre of the Pale, the part of Ireland directly under the control of the English government in the late Middle Ages.By the 19th century, Dublin had served as the centre for English rule in Ireland for centuries, and Dubliners were stereotyped as being heavily Anglicized and considered the most English of all the Irish.