Prelude and the Early WarEdit
Following the War of the Ancients, the night elves outlawed the use of all arcane magic in their forests, with execution as the penalty for use of the arcane arts. However many spellcasters did not agree with this and wanted to use their magic. Led by Dath'Remar Sunstrider these sorcerers decided to unleash a magical storm upon the tranquil forests. The Arch-Druid Malfurion did not want to execute so many of his own people and decided instead to banish them all from their homelands, and Dath'Remar led them across the sea to the east. These elves shrunk in height and their skin lost the dark violet hue common among their kin, and thus the Quel'Dorei, commonly known as the high elves, was born.
The elves traveled for years across the world that had been shattered by the wars with the Burning Legion, but in the end, they arrived in the lands now known as Lordaeron. Settling in the Tirisfal Glades they quickly encountered the locals, and while contact with the human tribes was sparse, the local trolls had built a great empire and attacked them on sight, quickly fueling a hateful feud between the two races.
Shortly after their settling, something evil beneath the earth started to drive some of the elves insane, so they decided to press on into troll territory. It didn't take long before the high elves founded the kingdom of Quel'Thalas in the northern forests, not knowing it was an area sacred to the trolls. The forest trolls attacked the fledgling nation in ever-increasing numbers, forcing the elves to use their strong magic. The superstitious troll warbands were frightened away and it was 4,000 years before they truly retaliated.
The Founding of StromEdit
The human tribes also suffered at the hands of the trolls. At the time the humans were factional people, scattered and leaderless. Chieftain Thoradin of the Arathi saw the threat to his race and decided to unite the humans. Along with his trusted friend and greatest general Ignaeus, later to be known as Trollbane, he devised a cunning strategy: fight the nearby human tribes, and after each victory offer them peace and equality. With this tactic, he united the tribes of the Arathi Highlands and founded the first of the human kingdoms, Arathor. Situated in what is now known as the Hillsbrad Foothills and Arathi Highlands, his growing empire ruled from the capital city of Strom. Up to this time, the human empire had rarely had contact with the reclusive, magic-wielding elves, and all contact with the trolls was through border skirmishes.
After years of continual besiegement by the trolls, the high elves, with defeat nearing, finally decided to seek the aid of the now-powerful humans of Arathor. The elven king Anasterian Sunstrider, a descendant of Dath'Remar, sent out their diplomats to try and negotiate the primitive humans into aiding them. Even though the elves had at times treated the humans no better than they had the trolls, Thoradin saw the danger in allowing the elf civilization to fall and agreed to an alliance. The elves would teach one hundred humans how to wield the arcane arts of magic, while the massive armies of Strom would mobilize and join the war against the trolls.
The Battle of the Alterac MountainsEdit
The armies of Quel'thalas and Arathor engaged the trolls in a great battle at the foot of the Alterac Mountains. The battle lasted for many days, but the knights of Arathor refused to give any ground, and finally, the elven masters agreed that it was time to unleash the elven and human mages upon the trolls. Magical fires from the sky hindered the trolls' regeneration, and their morale suffered. After some hours of the magical bombardment, the remaining human and elven warriors charged the trolls, broke their lines, and forced them into a terrible rout. Even as they fled, the trolls were pursued and butchered by the merciless allied forces. The trolls' power was broken and their population decimated, the last Troll empire lay in ruins.
The trolls would never recover from this defeat. The Gurubashi Empire had been shattered by a deadly civil war, and now the Amani Empire of the forest trolls was broken. What remained of the trolls of the northern lands was forced into the wilderness. However, the war was not completely unsuccessful for the trolls, thousand of elves and humans had been slain and the remaining left completely weakened. Thoradin did initially not want his people to use magic, but he was forced to accept it so it could be utilized against the incredible troll armies arrayed against him. This led to the foundation of Dalaran, and later many other city-states.
The elves owed the humans a debt of gratitude for saving their people and ending the first major war since the Sundering and War of the Ancients. This debt laid the groundwork for the Alliance of Lordaeron and was honored during the Second War when Anduin Lothar, last descendant of the King Thoradin of Arathor, led the Alliance to war against the Orcish Horde for the second time in his life.
The humans had the largest gains of the war: they were united and they gained a debt of gratitude from the only force able to threaten them. They were initiated into the arts of magic, their technology was greatly improved and inspired by the elves (some claim the elves taught them the art of metalsmithing, though it is more likely they knew of that before the war). They also became the greatest power on the continent and were able to spread in every direction with almost nothing in their way.
Adapted from Wowpedia.