Before the Horde
As noted, the Tauren are one of the ancient races of Azeroth. Prior to meeting the Orcs, the Tauren were a nomadic race, though it seems that they played little role in the grand dynamic of Azeroth for millennia. In fact, when encountered by the Orcs and their Warchief, Thrall, they were under significant pressure from the Centaurs and their tribes were separated. The Tauren do have a rich history which they have kept over the centuries, handed down over the ages through oral tradition; one such passage is as follows:

“Before the Age of Memory, the gentle Earthmother breathed upon the golden mists of dawn. Where the amber clouds came to rest, there were endless fields of flowing wheat and barley. This was the basin of her works – the great basket of life and hope. The Earthmother’s eyes shone down upon the lands she had breathed into creation. Her right eye, An’she (the sun), gave warmth and light to the land. Her left eye, Mu’sha (the moon), gave peace and sleep to the stirring creatures of the dawning. Such was the power of her gaze that the Earthmother closed one dreaming eye for every turning of the sky. Thus, her loving gaze turned day into night for the first dawning of the world. While the right eye shone down upon the golden dawn, the Earthmother’s gentle hands spread out across the golden plains. Wherever the shadow of her arms passed, a noble people arose from the rich soil. The Shu’halo (the Tauren) arose to give thanks and prayer to their loving mother. There in the endless fields of dawn, the children of the earth swore themselves to her grace and vowed to bless her name until the final darkening of the world.”

[edit] Allegiance with the Horde
The Orcs, led by Warchief Thrall, had come to Kalimdor seeking a land of their own, and in the course of establishing an early presence there, came upon the leader of the Bloodhoof tribe, Cairne Bloodhoof. Cairne sensed a great ally and leader in Thrall, and sought his alliance in fighting off their ancestral enemy, the Centaurs. In return, Cairne pledged his alliance to the Orc Warchief. For their part, the Orcs and the Jungle Trolls that composed the Horde found much in common with the Tauren. Each of these races wanted to achieve a more shamanistic culture, and the Tauren, long versed in the lore of spirit and nature, were well-prepared to provide counsel and support to the budding Horde. From then on, the Tauren became an inseparable part of the Horde, fighting with the Horde alongside the Alliance and Night Elves at the Battle of Mt. Hyjal, and later helped combat the forces of Lordaeron, led by Grand Admiral Daelin Proudmoore, when he attempted to invade Durotar.

[edit] Present
After the invasion of the Orc homeland of Durotar was repelled (as depicted in Warcraft III: The Frozen Throne), Cairne, with the help of the Horde, united the tribes of Tauren and settled his weary people in a new homeland, the lush plains of Mulgore. The capital city Thunder Bluff is built on a series of mesas which are connected to one another via rope and wooden bridges. At present, the Tauren are still ruled by Cairne Bloodhoof. However, even Cairne admits that he is unusually old for a Tauren (ninety-nine years old when he first joined the Horde), and the leadership of the Tauren may thus change very soon. Common wisdom hold that his successor will likely be Cairne’s own son, Baine Bloodhoof, but at this time such talk is simply speculation, particularly with the emergence of Elder Crone Magatha and her tribe, the Grimtotems, a tribe usually a distinctive midnight black in coloring, as a member of the Council of Thunder Bluff. The Tauren continue to supply fierce warriors and wise shamans to the Horde and are currently involved in the renewed conflict on Azeroth.