The Fall of Five Nations

Nobody actually “won” the Crimson Wars. Every nation was defending on multiple fronts, with shaky alliances being formed briefly only to dissolve once some sort of advantage was gained. The five original countries fought for several years, with more than two armies occasionally meeting on the fields of battle.
Meanwhile, as the nations expended resources, the Bright mages quietly gained followers and refined their abilities. They inserted themselves as important figures into each nation’s ruling bodies, and many became ranking commanders in their militaries. Slowly, they made themselves indispensable.
And then in mid-winter they struck.
Royal families were assassinated, generals of armies were murdered, and anyone with authority left was told to swear fealty to the Order of Luminance, or be eliminated. Those who fought back were killed mercilessly, sometimes entire platoons wiped out by a single spell. Within a week, there was no one left strong enough to oppose the Order or their own, and the Crimson Wars had left armies divided and unable to organize. The Order made their capital in Désakk, the city where the wizard Badrion Gutall lived. 
A major factor in the success of the coup was that the civilian attitude; the population at large across all five of the old nations were more interested in seeing an end to the bloodshed than they were in which group held power. Soon, however, bright mages held power in every city and large town, or held jurisdiction over several villages and hamlets.
Their control was absolute. Decisions handed down from the Order’s high council were to obeyed without question. The consequences for defying a bright mage became more and more severe over the years. Pleas for certain freedoms went unheard, and while small resistances did crop up from time to time they were quickly crushed. Within five years, the Order of Luminance had firmly established itself as an empire that spanned all of the original five nations.