@judgedread I've said this so many times by now it's tiresome, nevertheless:

Psychopaths cannot be negotiated with. You cannot sign agreements or treaties with them. They literally do not have the mental framework to maintain bargains even if they wanted to (and they don't). The best way to deal with them is killing them. All of them. If that is not possible for whatever reason you inflict enormous pain on them, preferably crippling them permanently, and you warn them that they will be killed the next time. If that is not possible you take control of something they value enormously and credibly threaten to destroy it.

These are the only tactics that modify their behavior.