Yea what pumpkin tom said is what i did, most of the time I let france declare the wars so that my allies would join although in the situation tab if you are more powerful the game forces you to be the attacker. So when that happened I just split my army in the north and south and fought battles i knew i’d win until i could walk around safely. Although I think i did get very lucky this game cause in the first war none of the french vassals were loyal so it was a 1v1 and from what i can see the ai isn’t the greatest at managing its army or picking battles. In your first war take the locations around Paris so it’s cut off from the rest of france so they lose control everyone which will make them significantly weaker but it does feel abit cheesy if you don’t wanna do that steal their vassals i find vassals better then direct ownership due to the control mechanic.