Answer
Llywelyn used the opportunity of John's arrest of Gwenwynwyn of Powys to annex southern Powys. Llywelyn was a Welsh prince who ruled over Gwynedd and Powys. In 1208, John arrested Gwenwynwyn, the ruler of southern Powys. Llywelyn used this opportunity to annex southern Powys, which had been disputed territory between Gwynedd and Powys. This annexation increased Llywelyn's power and influence in Wales.