The Echo Isles are a handful of small islands off the southeastern Durotar coast. For a while, the Darkspear trolls lived here, but when the Kul Tiras fleet attacked their land, they had to flee. They evacuated with the help of the Mok'Nathal Rexxar.
After the Third War, when the Horde settled in Durotar, Thrall made these islands off the southern tip available to the trolls. Recently, a Darkspear troll named Zalazane decided that the trolls did not need the orcs as allies and began practicing necromancy. He drove the Horde-loyal trolls off of the islands, converted followers, and created the zombies who now inhabit the Echo Isles.
Many attempts have been made to oust the powerful Zalazane and reclaim the islands but his forces are too numerous compared to the weakened Darkspear Tribe. They now live on the coast of mainland Durotar, in Sen'jin Village, as well as the Valley of Spirits in Orgrimmar, and in other scattered parts of Azeroth.