The Argon War began when the Argons rose from The Underworld and began terraforming and terrorizing the continent of Northern Shara.

The Argons are commanded by Shandra Manaya, the Argon Queen. The exact reason behind the Argons invasion is unknown, but it's clear they aim to eliminate all life and change the world of Arborea into something else.

The Argon War resulted in the creation of the Valkyon Federation, a coalition between all seven playable races in TERA. The Federation aims to defend all of Arborea and fight back against any who would harm the world.

The Argon War is the backdrop of a major part of TERA's storyline. The war is discussed and dealt with in the quest line: Argon War.