Llywelyn's 1205 marriage to John's illegitimate daughter Joan tied Gwynedd to the English royal dynasty. Joan could mediate between the two rulers, but family affinity did not prevent their relations from breaking down. In 1211 John recovered from an initial repulse, overran the Perfeddwlad, and burned Bangor. Welsh lords from South Wales and Powys assisted the invasion because they were willing to attack their rival in Gwynedd. Llywelyn had to seek peace and pay tribute, giving John the most successful royal campaign in Wales since Harold Godwinson's invasion.
Chapter · 15:11-15:52
John, Llywelyn, and the 1211 Gwynedd campaign
Marriage linked Llywelyn to King John, but their breakdown led to a royal campaign that exploited Welsh rivals and burned Bangor.