Battle of Thamasa

The Battle of Thamasa was a short and decisive battle between Imperial forces led by Kefka Palazzo and the espers, taking place moments after Leo Cristopheof the Empire and Yura of the espers had agreed on a peace treaty. In what can easiest be described as a genocide, Kefka turns nearly all living espers into Magicite before invading the Esper World to claim the Warring Triad. As the anti-Imperial forces are never able to get back on their feet following their defeat at Thamasa, the battle was essentially the beginning of the end.

Background
Hoping the espers could assist the Returners in their war against the Empire, Terra Branford opens the gate to the Esper World. However, the espers lose control of their powers once they cross into the human world, and fly off and decimate the Imperial capital of Vector.

Following the vast destruction, the Gestahlian Empire surrenders to the Returners hoping they could help prevent the espers from causing further bloodshed. A joint Returner-Imperial force go to Thamasa to search for the espers, and Returners eventually finds them in the Esper Caves. Their leader Yura is apologetic about the destruction they had caused, explaining that they were unable to control their powers once they crossed into the human world.

Yura and Imperial general Leo Cristophe meet face to face, and mutually apologize to each other for the destruction ther irresponsibility had caused. It doesn't take long for them to shake hands and agree to end the fighting once and for all; however, as everyone at the scene rejoyce, Kefka Palazzo enters the city.

Battle
Supported by two Magitek Armor soldiers, Kefka attacks Leo's troops, Returners and espers at the scene. Having recently discovered that magicite is more powerful than magitek, Kefka quickly kill Yura and the other espers and turn them into magicite. General Leo decides he cannot stand by while Kefka commits his crimes and attempts to stop him, but Kefka strikes him down after a battle between the two.

Responding to the cries of their friends in the human world, espers rush from the Esper World to their rescue. However, by now Kefka has become considerably stronger, and is able to kill all remaining espers and absorb their powers. Kefka's troops start torching Thamasa, but are then killed by Kefka's attacks.

Aftermath
With the Esper World now unprotected, Kefka and Emperor Gestahl enter it and use the power of the Warring Triad to raise the Floating Continent. Although the Returners manage to destroy the Imperial Air Force and make the Floating Continent accessible following the Battle over the Floating Continent, they are unable to reclaim the Warring Triad or to prevent Kefka from altering its alignment. As the alignment of the Warring Triad defines the shape of the world, by moving them Kefka triggers the End of the World. This apocalypse wipes out both the Imperials and the Returners, marking a de facto end to their war.