[mikestorrent]

There's something in-between law and suggestion, which is a Schelling point: https://en.wikipedia.org/wiki/Focal_point_(game_theory) ; these points can be influenced by information.

If we can establish, through published doctrine, what we will do in certain situations, then other nations can reason about our decisionmaking process. They can compare our actions to our policy, and make judgements about our trustworthiness as national actors. If we choose to act irrationally, or against our own doctrine, we become untrustworthy and other players have to adjust their game accordingly. That's the "enforcement" - and you can see this in action, e.g. with Mark Carney's recent speech.