Complex sentence: However Philip had failed in his attempts to occupy the Normandy islands in the Channel and the treaty held that "islands (if any) which the King of England should hold", he would retain "as peer of France and Duke of Aquitaine".
Split into simpler sentences: However Philip had failed in his attempts to occupy the Norman islands in the Channel. The treaty held that "islands (if any) which the King of England should hold", he would retain "as peer of France and Duke of Aquitaine".