So a reversal world?

nah not really

Old time ago the country was created by a group of adventurer but the descendants of the royal family grew afraid on how much power the frontier lord are gaining because of that they make the governing system that prever woman that lead to the noble gaining their lost power and weaken the frontier but bat noble that though of that law of the shield start using it to gain money by selling of the sons of their second husband to war for moneys, this result in the kingdom population slowly falling and the weakening of the kingdom border