View source for Talk:Alliance/@comment-26210945-20151027005735/@comment-27032150-20151029121147

You can't realy "choose" a faction, but you can pledge your allegiance to people associated with certain factions. If you do so, you can leave or defect the power you pledged to and choose another one.

but basically, you can rank up with every faction simultaneously, no matter if you are a member of a certain power or not.