In total, you can have 24 Quest Battlegrounds in the Saga storyline. To unlock further Saga Quests, first, you have to successfully attack and defend the available Battlegrounds.
Four or five levels of the regular Battlegrounds grant one level of the Saga Quest.
If you reached the required level of the Battlegrounds and still do not have new Saga Quest, make sure that all stipulations have been fulfilled:
1. Check if you have already conquered the previous Saga Quest provided in the Eagle Nest. Next, ascertain that you have claimed the reward and closed the corresponding notification in the Quests menu.
2. Complete all available quests to attack and defend Battlegrounds from the Quests menu (Warfare section):
