Contact your wiki manager. They are a liaison between you and Fandom staff. This is the exact situation they are there for.

It's very hard to give an advice with such a vague description of what happening.

Contact your Wiki Representative and they'll take care of the problem for you

No idea what is the poor decision you speak of so we cannot really say much... no one here can really help you stop this "civil war" or advice you further, besides you posted over there that you contacted staff before posting on this discussions page. Not much you can do beyond that, either the wiki manager or the staff you contacted will assist you.

As a Discussion mod, I would just delete stuff and lock like crazy, since it can be undeleted or unlocked. Also post a warning that stuff will get deleted or locked until an admin reviews it (and issues appropriate blocks).

If a mod lets stuff get out of control... guess what... it gets out of control.

If the wiki's administration is feeling overwhelmed by things going on in discussions, you can request for assistance from global discussions moderators.

What the others have already said is probably your best course of action if you really are concerned about a "civil war". But from what I see, I am guessing you are talking about Hydrozen? It seems they are the only admin and only bureaucrat to have edited in the past few months and they have been active throughout. It isn't like they just showed up a week or two ago after years of inactivity. As others have said, we really can't say much without knowing more about the situation (which we probably don't want to anyways). However, traditionally, the admins can do more or less what they want with the wiki except violate ToU, create overly restrictive rules (as judged by staff), or drastically change the focus of the wiki.

I've created a demotion poll for that admin, for your users to vote. If it gets enough yes, I'll ping your wiki manager on the poll and/or send it in a zendesk ticket