The Destruction of the Dark Portal, also known as the Final Battle at the Portal was the last battle of the Second War.
Though many orcs were killed or captured in the Siege of Blackrock Spire, many also managed to flee the field. The vast majority of these made haste for the Dark Portal in the south, slipping away through the Redridge Mountains. A pursuit was immediately organized by Turalyon, who had now assumed command of the united Alliance army after Anduin Lothar's demise. Their goal, however, was not necessarily to catch these stragglers. The exact location of the portal to Draenor (from which the Horde had launched its invasion seven years ago) still remained unknown to the Alliance's leadership. Thus, Turalyon hoped to follow the fleeing remnants of Doomhammer's army right to the unholy gateway itself.
The death knight known as Teron Gorefiend largely took command of the shattered Horde remnants following the defeat at Blackrock Mountain. He and his forces eventually reached the Dark Portal, at which point the pursuing Alliance fell upon them. After an extremely bloody battle (even by the standards of the Second War) the Alliance finally succeeded in destroying the dark gateway, with the remaining orcs slipping back to Draenor. The destruction of the Dark Portal would mark the end of the Second War in Azeroth.