You can enforce "no tribalism" by (a) requiring all users to either declare a tribe, or neutrality; and (b) requiring all posts containing tribal content to be self-marked as such.
For instance, suppose users can select in their profiles that they are either apolitical, SJWs, or shitlords. When an SJW or shitlord posts, they are offered a check box which indicates whether the post contains any virtue-signaling or shitposting, respectively.
Obviously, shitposts should be seen only by shitlords and so on. Political signaling at your peers is normal discourse and part of benign human social behavior. Political signaling at your enemies, or at neutral parties who just don't care, is normal human warfare behavior.
So the box is a self-reported box. But etiquette can easily render it mandatory. The chimps on each side of the river can and must suppress their own tribal instinct to throw turds over it, or the gods will rain down fire on the offending chimps or possibly even the whole tribe.
And of course, apolitical users shouldn't see any political crap at all...