The Kalos-Galar War was a war that took place around 3,000 years before the main-series games took place. The war began as a result of disagreements between the two regions after the empire that was based in the Seliosan city of Impome collapsed.
History[]
An unnamed empire had ruled over the continent that Kalos and Galar were a part of. However, it soon collapsed due to unknown reasons. Due to the rushed nature of its downfall, the two regions disagreed on who would rule the area that made up Kalos and Galar. As such, the two regions quickly made empires of their own and went into battle.
The war took a toll on both regions with several Pokémon and humans killed and several settlements ruined. Neither side was losing but neither side was winning. In the midst of this, the king of the Kalos Region: AZ' s Floette died in the war. Enraged by her loss, AZ set out to build an Ultimate Weapon which would end the war and bring back his Floette.
As a result of the firing of the weapon, millions of Pokémon and human lives were wiped out all to restore life to AZ's Floette while granting immortal life to the king himself. Shocked by AZ's actions, the Floette disappeared as AZ became distraught. Later, AZ's brother UZ buried the Ultimate Weapon.
Aftermath[]
The firing of the ultimate weapon had a severe impact on both regions. Several Pokémon species disappeared from the regions some of which had migrated to other regions out of fear. The nearby Floron Region to the north was affected as it mutated some Pokémon into Delta Pokémon which although had been there since the region's existence, affected the ecosystem greatly. The Selios Region too was affected with the northwestern areas of the region being devoid of Pokémon until the contemporary era where a resettlement plan took place. Even in far-off regions like Hoenn and Johto, several Pokémon species disappeared.
The firing of the weapon also alerted an Alien Pokémon called Eternatus which crashed into what is today Mittleford University in Galar. The energy released by Eternatus created the Dynamax and Gigantamax phenomenons along with the beginning of the Darkest Day.
Among all this, 2 Mythical Pokémon: Meltan and Melmetal that had been extinct since the prehistoric period were bought back to life with the energy created by the ultimate weapon.
Records of the ultimate weapon's firing were kept secret by Kalos and Galar for generations until the modern era. However in Floron, Selios and Jorigu, records were kept of the ultimate weapon's firing.