Question about Domaine Influence Card Action “Alliance” - What happens if the border marker between two allies is rotated 90 degrees?
The alliance continues. Rotating a border marker 90 degrees is only a reminder. If this reminder is removed by the a third player's expansion, another border marker between the allied Domains is rotated 90 degrees. If the border between 2 allied Domains is completely removed, it is on you to remember that these Domains are allied. Therefore, an expansion isn’t allowed in this case either.