Complex sentence: Thomas of Woodstock commanded one of the largest campaigns of the period after the Breton War of Succession, when English forces had supported John V, Duke of Brittany against his rival for the Dukedom Charles of Blois, supported by France.
Split into simpler sentences: Thomas of Woodstock commanded one of the largest campaigns of the period. This followed the Breton War of Succession, when English forces had supported John V, Duke of Brittany against his rival for the Dukedom Charles of Blois, supported by France.