From the mid @-@ 14th century , after the Black Death , Norman settlements in Ireland went into a period of decline . The Norman rulers and the Gaelic Irish elites intermarried and the areas under Norman rule became Gaelicised . In some parts , a hybrid Hiberno @-@ Norman culture emerged . In response , the Irish parliament passed the Statutes of Kilkenny in 1367 . These was a set of laws designed to prevent the assimilation of the Normans into Irish society by requiring English subjects in Ireland to speak English , follow English customs and abide by English law .