My idea its if you have friends of other clans, has a boton to challengers him to war, for example i ser 2th10, 5th9, and 8th8, and the game send that request to the other clan, this way they choose the same quantity to begin the war, but if they dont have the same quantity of th10 or th9 just the clan that challenge to war change the tipe of war changing the number of th to match the war with the same number of th10, th9, th8.....etc........
