18 February 1366: The Viceroy, Lionel Duke of Clarence summoned a Parliament at Kilkenny on this day. From this emerged the series of infamous ordinances that became known as the ‘Statutes of Kilkenny’ and were designed to put a legal framework on the division of Ireland into two separate peoples: the English and the Irish. It contained thirty-five chapters of note.
For instance if any man took a name after the Irish fashion, used the Irish language, or dress, or mode of riding (without saddle), or adopted any other Irish customs, all his lands and houses were forfeited, and he himself was put into jail till he could find security that he would comply with the law. The Irish living among the English were permitted to remain, but were forbidden to use the Irish language under the same penalty. To use or submit to the Brehon law or to exact coyne and livery was treason.
The Statute of Kilkenny, though not exhibiting quite so hostile a spirit against the Irish as we find sometimes represented, yet carried out consistently the vicious and fatal policy of separation adopted by the government from the beginning. It was intended to apply only to the English, and was framed entirely in their interests. Its chief aim was to withdraw them from all contact with the "Irish enemies"--so the natives are designated all through the act--to separate the two races for evermore.
From A Concise History of Ireland by P. W. Joyce