Complex sentence: He and the Spanish commanders were unable to cooperate, and he retreated into Portugal, where he constructed the defensive Lines of Torres Vedras which protected Lisbon, while he reorganised his army into divisions, most of which had two British and one Portuguese brigades.
Split into simpler sentences: He and the Spanish commanders were unable to cooperate, and he retreated into Portugal, where he constructed the defensive Lines of Torres Vedras which protected Lisbon. Wellesley reorganised his army into divisions, most of which had two British and one Portuguese brigades.