For warfare that is mostly indecisive, one possible settlement could be the border adjustement. This represents the loss of a few towns, villages, or fiefs on the border. This could have no impact in the game, and just be a face saving solution for the invader who agreed to abandon their invasion, but was not liable to take and hold a province. Or it could be resolved by adding one province level to one of the winner's provinces, and subtracting same from the loser's provinces. Since not all valuable settlements and raw materials are on the frontier, this could not go on forever. Also it doesn't work so well with small province levels. Another solution is to impose a province collection penalty and bonus for the loser and winner, which is temporary, and reflects the kind of adjustment that corrects itself over time.