Complex sentence: Elizabeth married Richard de Beauchamp, 13th Earl of Warwick before 5 October, 1397 he was the son of Thomas de Beauchamp, 12th Earl of Warwick and Margaret Ferrers.
Split into simpler sentences: Elizabeth married Richard de Beauchamp, 13th Earl of Warwick before 5 October, 1397. He was the son of Thomas de Beauchamp, 12th Earl of Warwick and Margaret Ferrers.