There's a great diversity of people and cultures living within the World of Warcraft. Many are members of the Horde or the Alliance, and quite a few others exist independent of these two confederations. Each of these races are known for different things, both culturally and in terms of innate abilities.
The Orcs are split into several tribes, and originate from Draenor. Though once overcome by demonic energies, under Warchief Thrall's leadership, they have attempted to return to their shamanistic heritage and start a new life in Kalimdor, in a wasteland dubbed Durotar in memory of Thrall's father. They are the nominal leaders of the Horde.
The bovine Tauren live in the grasslands of Mulgore. Tauren are not especially known for violence, but are incredibly fierce in battle once enraged. Their people were facing attacks from the Quilboar when the Orcs came to their assistance. The Tauren are indebted to the Orcs for this and faithfully serve the Horde.
The Darkspear Trolls share a similiar fate to the Tauren. Having been chased through the land by Kul Tiras marines and the Kolkar tribe of centaurs, they were also saved by the Orcs and now live beside them in Durotar. The Darkspear are but one of many troll tribes that live throughout Kalimdor and Eastern Kingdoms.
When the Scourge wiped out the Human kingdom of Lordaeron, it was the Forsaken (aka Undead) themselves that mounted a resistance to The Lich King after breaking the control he once held over them. Led by the former Blood Elf, Lady Sylvanas Windrunner, the Forsaken have driven the Scourge out of Tirisfal Glades and are in an unending war they cannot win alone. They provide much of the magic and brainpower to the Horde, although their aims are not completely clear.
The Blood Elves are Elf nobility that are addicted to arcane magic and have broken from the Alliance and follow their leader, Prince Kael'thas Sunstrider. Kael'thas followed Lord Illidan Stormrage through The Dark Portal into Outland and left most of his people behind. In his absence, their mutual struggle with the Forsaken against the Scourge has led them to begrudgingly join the Horde, and this assistance has enabled them to fight for, reclaim and hold their homeland in the Eversong Woods of Quel'thalas, Silvermoon City. The Blood Elf race was introduced in the World of Warcraft expansion pack, The Burning Crusade.
The hub of the Alliance is the capital of the Dwarves, Ironforge, in the snowy mountains of Dun Morogh. Having always maintained close ties with the Humans, King Magni Bronzebeard leads his people in a diverse coalition against the enemies of Dwarf and Human alike.
The Human race has been the cause of much of the strife in the world, but it is their skills in diplomacy that have brought together the Alliance of Dwarves, Gnomes and Elves. While there are many Human kingdoms, the only mainland sovereignty that is still in contact with the world is the Kingdom of Azeroth, with its capital city of Stormwind in Elwynn Forest. In the absence of their missing king, they are ruled by the Regent, Highlord Bolvar Fordragon.
Gnomes are a curious and inventive people whose progress with magic and technology has been incredible. Sadly, following an invasion to their home of Gnomeregan by Troggs, the gnomes response to the situation resulting in radiating the city and rendering it inhabitable. Much of the gnome race was lost during this tragedy, and the remainder live with the dwarves.
The Night Elf race is responsible for most of the history of the world pre-dating the first war of this time, and this has resulted in them remaining aloof and independent of the world for thousands of years. With the invasion of the Burning Legion during the third war, the Night Elves were forced to ally with the Humans and Orcs to save Azeroth. Since then, they have joined the Alliance and have rebuilt a new world tree of Teldrassil, northwest of Kalimdor.
The Draenei have suffered a long-tortured history at the hands of the Burning Legion. Having fled from one world to another, and eventually settling on Draenor, they were nearly destroyed by the Orcs after living peacefully together for many years. Prophet Velen's sect of the Draenei created a living ship known as The Exodar that left Draenor and eventually crash-landed on an island chain (Azuremyst Isle and Bloodmyst Isle) near Teldrassil. Brought into contact with the Humans via the Night Elves, the Draenei have joined the Alliance out of a mutual hatred for the Legion. The Draenei race was introduced in the World of Warcraft expansion pack, The Burning Crusade.
The ten sovereignties of the Horde and the Alliance are just a small part of the intelligent life in the world. Kalimdor is filled with harpies, quilboars, centaurs, furbolgs, and the insectoid silithids. The Eastern Kingdoms are rife with The Scourge, gnolls, forest trolls, kobolds, troggs, and Worgen. There are also many break-away groups that defy governments or wage their own holy wars, blinded by corruption or driven by a false hope of extreme divine power to rule over Azeroth and all its races.
There are also a good many other independent groups that are friendly, with whom you can gain a reputation as a hero.
Races that are not playable are listed under Category:WoW Mob Races