18. which of the following wars rejected in the beginning of the modern state system? a. the seven years' war b. the thirty years' war c. the war of spanish succession d. the war of austrian succession

B. Thirty Years War. This war was rejected by the European balance-of-power principle. The Thirty years war was a war over religion and killed 30% of Germany's population. The treaty that ended this war was Peace of Westphalia.