Long ago, before the Sundering, the land of Nagarythe was the shield of Ulthuan, the place where Aenarion set up camp during his successful campaign to obliterate the forces of Chaos on the island, where he made court with his new wife, Morathi. The long struggle against Chaos somewhat estranged the elves of Nagarythe from their southern kin: the proud and warlike northlanders saw themselves as the defenders of Ulthuan and their kin as having grown soft, the more refined elves of the south saw their kin as having become cruel and bloodthirsty in their incessant warfare, forgetting the dangers of the way of Khaine.
When Aenarion died, his son Malekith became King of Nagarythe and ruled for many years before the civil war, and his skill as a general inspired great trust from his people. Under the surface of a warlike people, the taint of Chaos had begun to spread, aided secretly by Morathi. The people of Nagarythe grew suspicious of one another, and many joined in the great purge of the Cult of Pleasure, their memories of the great campaign against Chaos driving them on to cut out any corruption amongst them.
And then came the day that Malekith declared his claim for Phoenix King a second time, and returned from the Shrine of Asuryan horribly burnt - by his enemies, he claimed. The majority of the people of Nagarythe believed his words, and soon the kingdom began to grow into an armed camp as pro-Malekith forces began to trickle in from Saphery and many other provinces of Ulthuan. When the civil war broke out into open conflict between Malekith and Caledor I, the armies of Nagarythe stood with the Witch King and achieved many victories, capturing Tiranoc and Ellyrion before the tide of battle turned against them.
However, there were some who stood against the pretender King, the wild and independent clans of the highlands of Nagarythe, who had long been suspicious of the decadence of the lowlander city folk and had always placed their loyalty to their clan chiefs above that to their titular king. When the war began, the highlanders waged an unceasing guerrilla war against their neighbours, and it was in Nagarythe that the civil war rose to its height of savagery and butchery, as both sides careened towards total war. Although the city-folk of Nagarythe were the more numerous and well-supplied, the highland clans used their superior knowledge of their rugged homeland to wage a campaign of hit-and-run strikes, vanishing back into their mountain fastnesses, and luring in Malekith's forces to be ambushed in the high passes.
When Caledor I defeated him at the Battle of Maledor, Malekith fled north to his fortress, from where he held council with his renegade mages and sought to destroy the Vortex - whether he believed he could control the raw force of the Aethyr within or whether it was the ultimate act of revenge, we will never know. However, the ultimate harm of the spell fell upon the very people who had supported the most. When the Sundering came, most of Nagarthye was sundered and fell beneath the wave. Only those loyal supporters of Malekith who had made it to safety inside his fortresses - which would become the Black Arks - were untouched by the calamity. But those who were outside the fortresses, the minority of the Nagarythi who had declared for Caledor, the Malekith supporters who had not made it to safety in time, and many no doubt who had remained neutral in the conflict felt the full brunt of the sorcerous blow.
Those who survived made their lives in a land that was a twisted mockery of what it had been, a wild place of jagged rock outcroppings and blackened trees, populated by a throng of monsters called up from the Aethyr - the Shadowlands as they are now called. The majority of the survivors were, unsurprisingly, the highlander clans whose lofty demesnes were spared the worst of the flooding that left the land infertile. The highland clans quickly took control over all that remained of their homeland, sending forth their warriors to subdue the wild beasts and keep watch for future invasions.
Over the years, as Druchii invasions after invasions crashed their way through Nagarythe, the highland clans of the Shadowlands forged themselves into a fierce and relentless band of skirmishers and guerrilla warriors, known to their southern kin as the Shadow Warriors. Of all the Asur, the Shadow Warriors of Nagarythe hold more hate for the Druchii than any other; of all the Asur, the Shadow Warriors of Nagarythe are among the few whom the Druchii fear as much as they hate.