Third Burning Legion Invasion of Azeroth

The Third Burning Legion Invasion of Azeroth (aka the Third Legion Invasion) was the Burning Legion's fourth major attempt at invading the planet of Azeroth, and its third successful one.

The conflict began with the orc warlock Gul'dan's alternate timeline-self rising the Broken Shore from the bottom of the Great Sea and opening the Tomb of Sargeras, which was the infinite demon army's gateway into the mortal plane. The Battle of the Broken Shore is widely regarded as the beginning of the invasion. Most of the conflict happened on the Broken Isles between Northrend and the Eastern Kingdoms.

After the tomb was closed, the invasion ended, but after a chain of events between Illidan Stormrage and Khadgar, the Legion homeworld, Argus, appeared in the sky via a planet-sized portal created with the Sargerite Keystone. This sparked another military campaign immediately thereafter.