Complex sentence: Dafydd ap Gruffydd, brother to Prince of Wales Llywelyn the Last, attacks an English castle; his brother feels compelled to support him despite poor preparation for war, quickly leading to the final English conquest of Wales by King Edward I of England.
Split into simpler sentences: Dafydd ap Gruffydd, brother of Prince of Wales Llywelyn the Last, attacks an English castle; his brother feels compelled to support him despite being unprepared for war. Their actions lead to the final English conquest of Wales by King Edward I of England.