Complex sentence: Both he and Pedro de la Plesa were caught by the Dutch Republic in a failed attempt to break through the imposed blockade at Dunkirk, he and de la Plesa leaving Captain Jan Jacobsen to face nine pursuing Dutch warships alone.
Split into simpler sentences: Both he and Pedro de la Plesa were caught by the Dutch Republic naval force as they attempted to break through a blockade of Dunkirk. He and de la Plesa were accused of leaving Captain Jan Jacobsen to face nine pursuing Dutch warships alone.