Complex sentence: The signatories were France, England, Holy Roman Empire, the Papacy, Spain, Burgundy and the Netherlands, all of whom agreed not to attack each other and to come to the aid of any that were attacked.
Split into simpler sentences: The signatories were France, England, Holy Roman Empire, the Papacy, Spain, Burgundy and the Netherlands. The countries agreed not to attack each other and to come to the aid of any that were attacked.