The Emerald Dream is basically the Dream of Azeroth and it is the Blueprint for all Worlds whether it be Planets or Cosmic Planes of Existence.
Azeroth according to Folklore was put to sleep while fighting the Old Gods themselves. The Titans extended her sleep by having Nymue control her Dreams to make them a Blueprint for Existence while making her think she is a Titan and not a First One.
The Titan Eonar has placed Nymue in charge of keeping Azeroth’s Dream from changing and thus her from awakening to placate Aman’Thul. Once Nymue is removed Azeroth will start to awaken from the sounds of things. According to the Automa Oracle in Zereth Mortis her voice will awaken the other First Ones.
The Eternal Ones of the Void have been scheming to corrupt her before the Nathrezim do. All the Cosmic Forces want Azeroth for themselves though it seems the Forces of Death have acknowledged that Azeroth herself might die.
The Nathrezim’s chief Agents for corrupting Azeroth to Death are Yogg-Saron(Spy infiltrating the Void), Lothraxion(Spy infiltrating the Light) and G’Hanir(Spy infiltrating Life) it would seem.