The Wars began when one of the Great Mages, Ma'ar began a quest for secular, rather than magical power. He built an army of followers and began instilling a xenophobic racism with his talk of a "superior breed." He united a dozen warring tribes, eventually rising to the position of Prime Minister to the King of Predain. When the king died without an heir, Ma'ar took the throne and began reshaping the kingdom.
Anyone officially declared a foreigner, such as Kaled'a'in like Amberdrake, were subject to ever tighter restrictions. Eventually Ma'ar began "deporting" them, though no one knew where. In all likelihood, they were simply killed. Ma'ar's campaign soon encompassed anyone who might oppose him as well as anyone who might oppose wars of conquest against their neighbors. They were tortured and killed or forced into slave labor.
Through it all, the Great Mages had taken little notice of what was happening until Ma'ar moved to expand his territory beyond the borders of Predain. By that time, he was nigh unstoppable. He and his armies rolled across Velgarth. Kingdom after kingdom fell to him until he eventually came up against the borders of Tantara.
Ma'ar followed his usual technique of weakening the nation from within by destroying the central government. In this case, he activated a fear spell in the middle of the royal palace. The result was to drive away nearly all the kingdom's leaders, including the king. They ran in a panic, then stayed away out of shame for their "cowardice." One of the few unaffected was the Lady Cinnabar. A Healer, Cinnabar slept under full mental shielding, and so escaped the spell. She called on the kingdom's Archmage, Urtho, for help. One of the Great Mages, Urtho took command of the kingdom and her armies, centering them on his Tower, and sending them out to battle via permanent Gates.
Unfortunately, Ma'ar was too strong, and he slowly marched his way across the kingdom, town by town. Urtho did his best to protect people, evacuating ahead of time. Eventually, Ma'ar took the Palace, and setup his headquarters there. Through treachery he poisoned Urtho. What he did not realize was that Urtho had placed the equivalent of a magic deadman's switch on his Tower. When he died, it would unleash a magical explosion destroying the Tower and everything in its vicinity.
Knowing his time was short, Urtho evacuated the area of the Tower, sending the people out through the Gate network. He gave Skandranon a weapon that would disrupt Ma'ar's magic, and hopefully destroy him in the unraveling. He intended Skandranon to use it at a later date, but Skan immediately infiltrated the Palace, detonating the weapon as Urtho died. The resulting double explosion became known as the Cataclysm.
With Ma'ar's destruction, the Mage Wars were finally over.