It's more correct to describe the collusion of the publishers as a cartel than as a monopolist here. They work together in collusive price-fixing arrangements.

It's more correct to describe the collusion of the publishers as a cartel than as a monopolist here. They work together in collusive price-fixing arrangements. Amazon may have just enough market power as a customer of theirs to break this arrangement, however it would be quite a stretch to call Amazon a monopsony.