Civil war broke out again in England in 1215 between forces loyal to King John and rebel barons, supported in due course by Prince Louis of France. John annexed the castle in 1214 and William sided with the rebels in 1216. King John responded by sending forces to attack the castle and successfully retook it. Despite John's death, the war continued until forces loyal to John's young son, Henry III, finally achieved victory over the rebels in 1217.