Answer
Llywelyn ap Iorwerth became the sole ruler of Gwynedd through diplomacy and warfare. He began by marrying Joan, the daughter of King John of England, in 1205. This marriage gave him the support of the English king, and allowed him to expand his power in Gwynedd. He also defeated his rivals in Gwynedd, including his uncle Dafydd ab Owain Gwynedd, in battle.