The Demonic Wars

The Demonic Wars (6000 - 3000 BE):

The Demonic Wars, or Demon Wars, were a series of incursions by fiends and devils into the realm of Alaesia. The fell beings attacked in waves every 500 years (6 wars in total), the most deadly of which being the First, Second, and Last Demon Wars.
 

The First Demon War:

The First Demon War occured at the turn of the millenia, 6000 BE (Before Empire), as several portals opened in the western Dragontooth mountains allowing them to flood the unsuspecting countryside with little response. The Demon armies were composed of Devil lords commanding fiendish armies that reaved over the lands, slaughtering innocents and razing towns and villages to the ground.
  The first people to be affected by the conquest were the neighboring Rock Dwarves, who lived within the Dragontooth Mountains and the Valley Halflings who lived in the neighboring hills. While some of the Halfling townships were able to escape the safety of the Wood Elves, the Rock Dwarven Kingdom of Flintpike was obliterated, any survivors forced into the high alpine regions for remainder of the war. Due to the following events in the Second Demon War, the descendents of the Flintpikes would not regain similar population levels for the following 2000 years.
  After the Valley Halflings warned the Eastern Wood Elves of the coming hoardes of monsters, an Eleven army was mustered and met the Demons in battle at the edges of the their forests, driving them back after six years of bloody fighting. However, the Devils were not vanquished and regrouped, marching towards the southern lowlands and laying waste to High Elven cities and trading posts. The High Elves, who had previously refused to aid the Wood Elves in what they considered "their fight" were totally unprepared and faced heavy casualties. They spent the next two decades fighting and exterminating the remaining Demons with their lands in total devestation. Facing a gender imbalance and a shared experience with their northern Elven compratriots, tensions were able to ease between the Elven races and led to intermarriage and trade agreements.
 

The Second Demon War:

The Second Demon War followed a period of genuine peace and constructive rebuilding by the Elves and the Halflings. Even the Flintpike Dwarves were able to make a resurgence, selling lands to the newly arrived Isauran Men, Humans from the far northeastern isles of the Cold Sea. A peace which, indicated by the name of this sub-section, was not to last. On the turn of 5500 BE exactly, the Demons returned, their old portals reawakened and the worst of the Devil commanders reincarnated. One more, the Flintpikes were annihilated, those left fleeing once more into the alpine regions, or some to the trading towns and logging camps of the Isaurans.
  It is here where history diverges (as all Isauran history is shrouded in myth), some say that the disperate Isauran townsfolk immediately retreated from their towns and residences to seek the help of the Elves, while others say that some meager defenses were placed against the Demons before being slain themselves. In either case, the Isaurans beleagured by war approached the Wood Elves of the forests to East for protection and aid.
  As the demons raided the hills and valleys causing untold misery, the Elves called a meeting of races agreeing to the formation of the Elven Trinity, a council of the three Elven Races: High, Wood, and Occasian. The Occasians were an extremely arrogant and isolationist tribe that lived in the Northeastern Isles of the Cold Sea, and it is said (and often joked) that they only joined the Trinity because the Isaurans threatened to return to the Isles.
  Once a coalition was formed the united Elven armies, accompanied by Isauran mercenaries and adventurers met the Demons in pitch battle and following the the lessons of the previous war, annihilated the last of Demons within 8 years of their emergence from the portals.
 

The Middle Wars:

The Middle Wars refers to the 3rd, 4th, and 5th Demon Wars which were all dealt with within a year of their begining. As 500 years past after the 2nd War, the Isauran Humans developed into a healthy Kingdom that incorporated the lands of the Halfling townships and even purchased some of the forests from the Wood Elves. A strong kingdom they readily rejoined the coalition at the offset of each Demon War and helped defend Alaesia. A plan was put in place that the Human armies would bait out the Demons into the vallies immediately after they left the portals and the armies of the Elves would fall upon them from the hills surrounding them.
  This plan worked with smashing success each time and the threat of the Demons seemed to fade in the minds of Men. Keeping good relations with the Flintpike Dwarves, they respected the coalition and respective monarchs always honored the call, welcoming all members to their capital after each war to participate in celebration. A notable focus of celebration was after the 5th Demon War, for the Great High Elf, Tiberius the Honorable, who single-handedly defeated two Devil Lords in hand-to-hand combat.
 

The Last Demon War:

The Last Demon War followed the events of the Myth of the Isaurans found here: https://www.worldanvil.com/w/alaesia-lynarm/a/myth-of-the-isaurans-ethnicity
  The events of the High Elf attack had left the Isaurans in shambles, they were down to their last four major cities and as the millenia dawned the Demons emerged once more. The Queen of the Isaurans sent her people into hiding and fought one final battle against General Tiberius, seriously delaying them from reaching the last of her cities, as well as the Demon portals themself.
  The Demons returned to Alaesia to find an unusual sight, a Dwarven ambassador from the Flintpikes, asking for a truce of non-agression, and the Devil-Lords agreed. For the Flintpikes had witnessed what happened to their long-time ally and refused to fight side-by-side with the High Elves, much to the chagrin of their fellow Dwarven brothers who denounced their cowardice. Eventually they would come to be known as Dark Dwarves due to their actions.
  The war following was a gruesome one, the Elven army, severely weakened over two decades of fighting was only able to hold the Demons off from entering past the hills outside their portals because of a desperate charge from the Valley Halfling mounted slingers which shocked the strategic Devils enough that Tiberius the 'Honorable' was able to slip through their defenses and destroy the portals while they were still open. He claimed to have used a high-level force spell to crumple the portals in on themselves. However it was done, it stopped Demon reinforcements from arriving and he was able to mop up the shattered Demon army over the next 8 months. Thus earning himself the title, Tiberius 'the Demonslayer'.
 

Lasting Affects of the Demon Wars on Alaesia:

The Demon Wars remain a core memory for most of the more elderly of Elves and the Elven Coalition and Trinity formed from then still exists at the time of the Empire. The annihilation of the Isaurans by the Demons led the Wood Elves to help grow and form the Silvan Men, Humans born of Elves and scattered Isaurans, who eventually spread far across the contienent and make up the largest population of the Empire of Alaesia in present-day. Furthermore, any remaining Isaurans were left to their own devices becoming mobile traders and nomads constantly on the move. The Dwarven lands remained largely the same after the Fall of the Demons, other than the ostracization of the Flintpikes.
  Other than long burnt-out and overgrown ruins, there are very little lasting physical sites from the Demon Wars. The new Silvan Humans never even experienced any of the wars and so its history is often far from their minds.