To invade another groups territroy (which will deffinately happen at some point) you firat need the Dominant Female to say that they are going ato invade/attack, and which group. Once she has posted "they crossed over to the other's territory", or words to that effect, all members have to go to that groups current roleplay day, where the fight will happen. We do it like that because that topic is kinda like the groups territory. When one of the groups retreat, both groups return to their normal roleplay topic.
If you want an example look at The Willows and The Devils, Roleplay-10th of July