The Neathian-Gundalian War was a conflict between the Neathians and the Gundalians that started before the events of Bakugan: Gundalian Invaders. It began when Barodius and the Twelve Orders invaded the planet Neathia in order to take the power of Sacred Orb to use it for evil; while the Resistance and the Vexos (with the Bakugan Termination System) fought for their occupation on New Vestroia. After the Brawlers joined the Castle Knights, the war went much better for the Neathians.

Prior to episode 30 of Gundalian Invaders, the war was taking place on Neathia, but in episodes 30-34, the battlefield has shifted to Gundalia, where the Brawlers launch a counter-invasion, but in episode 35-36 the battlefield has shifted again to Neathia, while there was only one battle left in Gundalia between Kazarina and Fabia, Nurzak, and Mason. Now that the Twelve Orders have been defeated and that Nurzak has promised to be in alliance with one another, the war is consequently over.

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