Humans started as the good guys in the Warcraft saga, forced to battle against the evil and chaotic Orcs in the first two games, Orcs and Humans, and Tides of Darkness. In warcraft III: Reign of Chaos, the humans become more of a neutral race, committing both good and evil acts. This brings us closer to out real world understanding of Humans, that there is no black and white, just shades of grey.
In terms of game story, the Humans started as peaceful beings throughout the Eastern Kingdom, and were forced into a militaristic role when the Orcs came throughthe Dark Portal. The two races have been in conflict ever since.
The Orcs were victorious in the first great war(cronicalled in Warcraft I) killing the Human king, sacking Stormwind keep and forcing the humans to retreat Dunkirk style, across the Great Sea to Lordaeron. In the second war(Tides of Darkness) the Humans formed the Alliance, which consisted of the seven human nations, the elves, the dwarves and the gnomes. The Humans have the upper hand in most of this battle, driving the Orcs back and closing the Dark Portal(even though they were betrayed by Alterac, one of the Human nations).
The victory was short lived, because with no common enemy the Alliance crumbled back into it's component parts, and when the Orcs reappear in Reign of Chaos. Thrall escaped from his enslavement to reform the Orcish Hordes, the Undead sweep across Lordaeron, Prince Arthas Menethil is corrupted by the horde and slays his father.
Arthas's lover, Jaina leads an expedition of the Alliance races to Kalmindor, allies with the Orcs and Night Elves and defeats the scourge and the Burning Legion.
In the World Of Warcraft, the once dominant humans are scattered around the world, disconnected and disorganised.
Todd O'Donnell admits to playing far too many games. After initial focus on power levelling he has spent much time developing guides and hints for World of Warcraft Players which can be found at his Warcraft for the People [http://warcraft.gumptiongames.com] website