Which of these is the strongest example of multilateral foreign policy?

one nation states publicly that it will refuse to trade with any nation that criticizes its leader.
one nation refuses to trade with a rival nation because it does not allow women to vote in an upcoming election.
two rival nations go to war with one another over disputed territory.
two allied nations enforce economic sanctions on a country until its government changes a key policy.

The answer is  "Two allied nations enforce economic sanctions on a country until its government changes a key policy."

Explanation:

Here we see a foreign policy move coordinated with a partner, none of the two allied nations acts alone in imposing sanctions on the third nation. Among options shown here, this is the best possible example of a multilateral policy.

on my last question

social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they liv