Bσσk Oиє+Oиє: иσт тнє Bєgiииiиg

[Kendra, The Guy Who Comes Up With Stuff]

For centuries, the tribes lived in peace and separation. It was, in fact, much as it is today, but with less technology. While there was some trade among the nations, on the whole they kept to themselves. Except for First Lectra, whose individuals teleported all over the place and had wild parties while trespassing on other nations' lands. But they were mostly harmless, and the others found them endearing and no harm came of it. They got along especially well with First Ventis, who actually built their only permanent structure as a party-house for whenever the Lectrans felt like popping in (the Ventisians weren't always there, but it was a great gift). That is when the Cruel Sides of the elements began cropping up.
First Ignatia was the first to find the other side of their powers, the forest fires that had helped forests grow and the forge fires that allowed them to do extraordinary things with metals could also be used as explosive attacks, flaming projectiles, and roaring offense. While others banned their Cruel Magic, Ignatians never did.
The Ventisians found that, when working together with multiple elementalists (this took them a LONG time), sometimes even with a fire wielder if the Ventisian was strong enough, they could bring powerful tornadoes down. In First Ventis, this was almost harmless, as basically everyone was capable of surfing the twisters and even saving whatever items had significance. This is probably why they became careless with it later. After pressure from the Terrans, their food suppliers, the anarchists eventually decided that common courtesy was to stop others from using Cruel Magic if they were seen, and, since Ventisians fly basically everywhere, the Cruel Magic wielders eventually gave up and went back to normal magic. This effectively worked like a ban, but it took a long time to get the free-spirited Ventisians from creating something even CLOSE to a law.
Etrans, beyond the peaceful waters of ponds and the marvelous flow of rivers, learned to cause rapids, flash floods, whirlpools, and even hurricanes when teaming up with Ventisians. Their Cruel Magic was the fastest to be declared illegal, as beyond being destructive, it was fueled by something different from their other magicks. Whatever the magicians bringing rapids, floods, and hurricanes were using, it was not a feeling of peace. The emotion they were drawing from has been lost to the generations.
Terrans were probably the most peaceful, as it took dozens of them to create earthquakes. Beyond that, telekinetic control over rocks and mounds of earth was the most offensive magic they had, and most could dodge the slow-moving fists that had to be massive and visible to be effective at all. They passed a quiet ban on their Cruel Magic (really just earthquakes) that hardly anyone opposed.
Lectrans' powers were always deadly and often got out of hand. Truth be told, there was really no way to police anyone from using Cruel Magic, as it was really just their normal magic used against other people. Murder and assault were already crimes, though, and intentional assailants soon found themselves defeated (though their teleportation meant that it took them forever to catch the criminals).
Shadow, shadow, shadow. Theirs was the most dangerous of all. After discovering the psychological side of their powers with dreams and nightmares, a few of them learned suggestion spells, putting their own thoughts into someone else's head but making them "sound" like that person's own. This was mostly harmless, as they would use it to get out of punishments for minor offenses most of the time. Then Garuneko took the next leap forward: He slowly brainwashed a legion of the mages of other tribes (fellow Darks had strong resistance) through a series of psychological tortures and thought transplants. With them at his side, he created a hurricane that spanned the entire continent, with twisters forming within it at random intervals. Lightning intentionally targeted humans and shot to kill. Wildfires raged as much as they could in the hurricane, the winds making them far worse. Earthquakes ravaged the other tribes, especially devastating the Terran underground world, burying entire cities alive. Forced to abandon their homes, all of the First Nations were systematically destroyed and the elementals all became refugees from what was far too one-sided to be a war.
Garuneko's power allowed him to channel raw emotion into his forces, practically giving them power as his own grew from the massive terror throughout all six family groups.
Then the six siblings, the First Elementals, came down to earth to face him themselves.
Garuneko's armies faced them head-on. Ignate, with all his ferocity, power, and skill with spears and swords, was washed away in the waters of the hurricane. Etra attempted to push the waters away from her brother but left herself open to a lightning strike. Terra halted several earthquakes but was covered in a wildfire that he barely survived. Lectra had tremendous energy and fought on for hours, teleporting around to become an almost impossible-to-hit target, but eventually a twister slammed a boulder into his head and he fell into a daze. Venti was the last to be defeated, managing to stay above the hurricane for hours before Garuneko himself launched a mental attack on her, sending her the feeling of being caged, trapped, helpless. Claustrophobic in the open sky, she fell to the earth and was also defeated.
But Shadow had been walking among the forces invisibly, touching the minds of all of Garuneko's soldiers. His siblings had fought long, and he had plenty of time to plant seeds that would steal the spell that had caused the mental damage in the entire legion. By the time the evil Dark Mage realized that he had missed a sibling, Shadow had planted the seeds of healing into all of their minds and activated it just as Garuneko undid Shadow's invisibility. The Dark Mage's armies immediately fell into a deep and restful sleep, to awaken free of the Cruel Magic clouding their thoughts. The spells that had bound their minds all fell into Shadow's left hand: The brainwashing of a thousand troops at his fingertips.
Garuneko's powers rapidly faded as the skies returned to normal and the water from the hurricane all crashed down at once, no longer held up by his army. The fires went out and the earthquakes stopped, the twisters stopped turning and the floods settled into peaceful seawater.
The power drain was so rapid that Garuneko fell to his knees and was too afraid to cast even the simplest of cantrips. The patron of Garuneko's tribe stood above him, holding boundless evil in his hands. A dark and subdued anger radiated from Shadow, and Garuneko felt more terrified than is technically possible.
"You have forsaken your gifts. You have perverted the power of your ancestors and brought madness to innocents."
"Please... please... I am your kin, I am a Dark... I-"
"You are guilty!" And Shadow hit the creator with his stolen madness.
All of it.
His mind torn into a thousand pieces, Geruneko tore off his robes with his fingernails and screamed like a banshee, tearing at his own throat with his fingernails until he took it out. Even then he did not die, and he continued tearing into himself until he removed his own stomach, and heart, and eyes. It was only then that Shadow felt a hint of mercy and allowed the mage to die.

New Civilizations were made in what continued to the modern day. Darks were distrusted by all but the Terrans, who remembered that it was Shadow himself who had saved them. The Darks were welcomed into Terra with open arms, but were still held in fear by the others.
That was fine with them, though. It gave them power.

As for the siblings, they, too, felt nauseous about how Shadow had killed the sorcerer, but the man had been so evil that none of them could say that it was disproportionate, or undeserved. Ignate was actually of the opinion that Shadow should have forced the dead mage to eat his own organs before allowing him rest, but he backed down quickly after the looks of disgust from Etra and Terra.
Since then, peace has been found, those who rediscovered the Cruel Magic were quickly defeated by a coalition of elementals, and nothing like that has ever happened since. A new Golden Age has come since then, and the Darks are actually beginning to be treated with less fear as the memories of what happened and the scars on the people's minds have faded.