Complex sentence: The Duke of Lancaster, John of Gaunt, refused to garrison it in 1377 five years after he took possession of the castle, asserting that he was wealthy enough to rebuild it if a French attack destroyed it.
Split into simpler sentences: The Duke of Lancaster, John of Gaunt, refused to garrison it in 1377 five years after he took possession of the castle. He asserted that he was wealthy enough to rebuild it if a French attack destroyed it.