When the Kingdom first came into contact with the Nation of the Night, 1500 years ago, neither was sure what to make of each other. The Nation was large, decentralized and pragmatic; the Kingdom was small with heavily populated cities and a tiny but very well equipped army. Because each had become self-sufficient, and their armed forces were about equal in strength, they had no reason to fight. For the most part, they ignored each other, coming together only to trade luxuries.
The only conflict that took place for 500 years was a massive engagement between the Nation and the Northern Provinces. While the warriors of the provinces were each mighty, they just couldn't hold against the massive numbers of National troops and crumbled. The Nation, not wanting the Provinces to rebuild and seek revenge, buried the provinces most sacred artifact, the Scepter of Thorin, so that none could rule over the provinces. Without a head figure, the provinces began to quarrel among themselves and eventually broke down into tribal villages.
The desert, on the other hand, was impassable to anyone, as the tribes would brutally attack any travelers. Separated from the eastern nations by these savages, the Western Lands of Tir Coill had no reason to change. And so, they didn't.
In all systems of hereditary rule, a tyrant will eventually take power. 500 years after the Nation and the Kingdom first made contact, a deranged madman took the throne of the Kingdom. Almost as soon as he put on the crown, he declared all citizens of the nation heretics, saying that their worship of the darkness was an insult to the light. After conscripting almost every man in his kingdom, he lead the entire army north to attack.
Caught completely off guard, the Nation fell apart. Their massive army was spread across their empire, taking away the only advantage they had over the Kingdom. The army of the kingdom marched across the plains, buring the entrances to the subterranean civilization, slaughtering its people, burning its farms and doing everything in its power to make the land uninhabitable. While some escaped the genocide by fleeing into the northern mountains, the Kingdom's victory was still complete, the nation would never rise from the ruins.
Now that the land to the north was open, the Kingdom began to expand in all directions. It made contact with the shamanistic island peoples of the eastern sea and began to trade their excess goods for spices and herbs not found on the mainland. The king began to send patrols into the desert, and slowly brought their influence to the wandering tribes. Eventually, one tribe grew above the rest and the Kingdom of the Sand was founded, finally bringing order to the region. Now that it was safe to cross the desert, contact with the west was established about 100 years after the Nation fell. Initially, the Coillians were completely unwilling to adopt the culture of the kingdoms, and this sparked violence. In the first few engagements, the well-trained and heavily equipped troops of the Light and the crafty, battle-hardened troops of the sand completely destroyed the peaceful druids of Tir Coill. This did not last long. The quick-minded people of the west began to forge better weapons and use the same styles of combat that the kingdoms used, mixing in their own hunting strategies. These new warriors founded an order they called "the Sidhe" and began fighting back. Their ability to silently and quickly walk through the densest forest quickly overtook the kingdom's forces, who relied on paths and roads for movement. Within a year of the initial fighting, the Sidhe Warriors had brutally slaughtered thousands of troops from each kingdom, pushing the invaders back to the desert.
After some time had passed, the Kingdom of the Sun once again contacted the Coillians this time taking a more diplomatic approach. The Tir Coill's villages were eager to show their hospitality and forgiveness, so they accepted the ambassadors with open arms. The Kingdom quickly realized the wisdom of this new approach, as the villages were now closer than ever and the Sidhe had expanded from a small group of hit and run fighters into a massive army of the forest. The culture of the kingdom began spreading once again. While they never gained the same kind influence they had over the desert, the westerners happily began to adopt eastern architecture and farming methods. For the next 800 years, they would still live in small druidic communities, but now they lived off of small farms instead of as hunter/gatherers.
Rise of the Magi:
When the Kingdom destroyed the nation, they didn't bury all traces of it. Recovered from the smoldering ruins were many encrypted scrolls. It took 200 years to decrypt them, but it turned out to be well worth it, for the scrolls contained the Nation's knowledge of the arcane arts (though the knowledge of darker magicks was lost to time). The King's scholars studied these day and night for another 25 years before finally founding the Sorcerer's Guild. These brilliant men and women learned to use the energy of the cosmos to do just about anything. They spread their influence throughout the Kingdom and beyond. When the first group of sorcerers reached Tir Coill, they realized just how powerful the druids of the land were, and resolved to mix the arts of sorcery and druidry.
This union provided mixed results, creating a caster that utilized the elements themselves in their rawest forms. The new sorcerers did not have the raw power or utility of the older sorcerers, nor did they have the control over the forest that the druids did. Deeming their experiment a failure, the sorcerers departed from the west returning home, leaving their results behind. The new casters, resentful over their former teachers' assessment, began to call themselves "magi" and founded their own guild. Over the next three-quarters of a century, the magi grew powerful in their own right. While they weren't as adept at destruction as the sorcerers could be, they turned out to be much more durable. this allowed them to fend for themselves on the battlefield, where sorcerers needed protection. They ended up growing so powerful that the Sidhe declared them honorary defenders of Tir Coill, and the magi swore to join the warriors in defense of their homeland should the need ever arise.
The Second War:
The discovery of magick was a great blessing for the people of the west, it caused unrest back in the east. Some members of the Kingdom believed that using the magicks of the Nation was blasphemy. What started with civil unrest eventually progressed to widespread demonstrations, than to scuffles in the streets and eventually to open warfare between the opposing viewpoints. 700 Years after the Nation fell, they finally got their revenge; a powerful diplomat took control over the northern half of the Kingdom and declared that the king had lost his right to the crown because he allowed the use of magick. The Kingdom splintered, the North, not allowing magick, the South, more liberal with their laws. The Kingdom of the Sand once again declared war on the West and officially allied themselves with the zealous North and in return, conquest of the West was promised when the South fell. Initially the fighting was fierce and bloody, but as people fled north or south according to their respective beliefs, the fighting slowed and it quickly became a stand-off.
For the past 250 years, neither side has made any significant gains or suffered any significant losses. In the West, the Sidhe, Magi and newly formed Hunters have made a mockery of the Desert's declaration of War, no battles have taken place and civilians of both sides travel freely through the other's lands. And in the East, the massive walled cities of the south kingdom stand strong and the overcrowded slums of the north are more populated than ever.