Complex sentence: He served in the large army which invaded Scotland in August 1400, led by the King in person: the aim of the invasion was to persuade King Robert III of Scotland to acknowledge Henry IV as his overlord.
Split into simpler sentences: He served in the large army which invaded Scotland in August 1400, led by the King in person. The aim of which was to persuade King Robert III of Scotland to acknowledge Henry IV as his overlord.