After all, battles are only a forceful way of obtaining a treaty. The English king wants to become the French king and to do so he must control enough French territory to make his coronation as French king convincing. There is a legal system built into the game, covering both civil and church matters. You can be declared an outlaw or excommunicated. You can even be tried and executed.
Money plays a large role in the game.
Money is important in this period. Troops were the biggest expense. The feudal levy could still be called out, but only for local defense and only for a limited period of time. Thus the object of taking your army into the field was not battle, but plunder. Sort of like a game of Monopoly with edged weapons.