From the 1940s onwards, the non-Welsh-speaking population grew in Welsh-speaking areas, resulting in Anglicisation on the periphery and then in the interior of these districts.
O’r 1940au ymlaen, cynyddai’r boblogaeth ddi-Gymraeg yn yr ardaloedd Cymraeg, gyda Seisnigo ar gyrion, ac yna ym mherfeddwlad, yr ardaloedd hyn.