To be fair, its an extremely flawed idea that letting the big guy win will just result in infighting because of the same reason now, it will still end being gangbangs unless you spend a lot of time on diplomacy which means peace for awhile. Medieval nobles weren't just like !@#$ the realm and all the power I hold, let's go attack a realm that will result in the destruction of my realm.
You're right, they made up reasons to go fight other nations, or fought wistfully in the name of religion, or because so and so insulted your cousin, and didn't marry your sister the Queen of the other nation.
