War of the Magi

"“The ancient War of the Magi... When its flames at last receded, only the charred husk of a world remained."

- A Final Fantasy VI intro cutscene (about the War of the Magi).

The War of the Magi (魔大戦, Mataisen) was an ancient and calamitous war fought 1,000 years before the events of Final Fantasy VI. This horrific event, almost destroyed the entire world, has thrown humanity back several centuries and created the preconditions for the actual game events.

In the Beginning
The 3 deities known as the Warring Triad descended from the heavens and fearing one another's power, began to war. The mortals caught among the fighting became Espers and were forced to fight as slaves to the gods. The gods realized the chaos their fighting was causing and agreed to seal away their power. With the last of their fading magic, the gods returned the Espers' free will before petrifying themselves. The last words they left to the Espers were: "Never must we be woken."

Espers and humans lived in peace for a time until another war broke out when humans attempted to seize Esper power for themselves. Espers and humans warred and humans infused with Esper magic came into existence, called "Magi". A battle of the war took place inside the Ancient Castle where the king, an esper named Odin, was petrified defending the castle from enemies, including enemy Espers and a powerful sorcerer. The Esper Valigarmanda was frozen and buried to be discovered a thousand years later in the Narshe Mines. Various other Espers became magicite and their shards were lost to the world.

There came to be two "Ultima Weapons": the first was a destructive monster with incredible magical powers, and the other was a powerful sword, which took its power from the user's vitality.

As the war drew to a close the Espers created a new realm where they could live in peace and fled there en masse, taking with them the statues of the Warring Triad. Left to their own conflicts, the humans turned on the magi believing them to be the cause of the war, and many were hunted down and killed. A few escaped and founded the remote village of Thamasa. With the Espers and magi gone, magic faded from the world and into legends.

Aftermath
A thousand years later the Gestahlian Empire seeks to exploit the powers of the Espers via Magitek, which could lead to a second War of the Magi. The Returners ally with the espers to destroy the Empire, leading to a smaller scale war that crushes the majority of the Empire, but the Empire's leaders, Emperor Gestahl and Kefka Palazzo, still aspire for power and feign defeat to capture and absorb the powers of the Espers that destroyed their capital, Vector. The two enter the Esper Realm and find the Warring Triad and raise the Floating Continent. Kefka disrupts the Warring Triad's balance of power shifting the World of Balance into the World of Ruin, in an event known as the "end of the world".

Trivia

 * In Latin, Magi is plural of Magus, which means "wizard". Magi is also a term used since at least the 4th century BC to denote followers of Zoroaster, or rather, followers of what the Hellenistic world associated Zoroaster with, which was—in the main—the ability to read the stars, and manipulate the fate that the stars foretold.
 * Final Fantasy VI is mentioned that Humbaba, Deathgaze and the Eight Legendary Dragons are ancient monsters sealed within the earth that are unleashed at the end of the world. Given that all of them are powerful magical beasts, they likely existed during the War of the Magi, but their exact origins and possible role in the war are but unknown and difficult to judge.