- It's considering as a flank army so in this case it must attack from an adjacent space ?
- Or we simply can't deliver an allie city by breaking a siege ?
And other question : Can we finish a mouvement on an empty allie city space ? And retreat outside the wall if necessary ?
See the Living Rules:
Allied forces may not stack together. They may move through each other without any MP penalty or having to battle, but may not end movement in a space with another power’s CU and/or leaders.
PLAY NOTE: This stacking restriction means you cannot attack an enemy army sieging an ally’s city, if the ally has CU inside the city, because if you are successful two allied forces would end the movement phase in the same space. While prohibiting such actions may seem arbitrary it was done to prevent writing a multitude of exception/restriction rules just to cover this one situation.
DESIGN NOTE: Coalition armies were rare in the ancient world during this time period. Even during battles where two powers were attacking a common foe, the forces tended to be separate entities. The use of a Campaign card simulates this type of action. (9.5.6)
However, if you use a Campaign Card the Living rules state:
9.5.8 Coordinated Attacks and Allied Armies: Allied armies can coordinate attacks with each other as the flanking army is not placed in the battle site, which would violate 16.2, but is instead placed adjacent to the battle site. A player may play a campaign card to sortie, 13.4.1, and then activate an allied army as a flanking force to aid the battle.