Complex sentence: After the death of the Welsh prince Llywelyn the Great in 1240 the English extended their authority into Wales as far north as the Conwy River from the result of three military campaigns to expand the royal lands of the County of Chester.
Split into simpler sentences: After the death of the Welsh prince Llywelyn the Great in 1240 the English extended their authority into Wales as far north as the Conwy River. This was from the result of three military campaigns to expand the royal lands of the County of Chester.