The tauren have often been viewed as the "good" guys of the Horde. While the orcs, blood elves, forsaken and trolls have all had various unsavory qualities, the tauren race stands out as a genuinely peaceful, altruistic race of spiritual people that want nothing but what's best for the earth and the spirits it contains. Despite their seemingly good intentions, this does not leave the tauren without conflicts of their own, and when a closer look is taken at their current activities, some questions still beg to be answered. The history of the tauren is arguably just as lengthy as that of the orcs or the blood elves, the major difference being that the history of the tauren race isn't really documented anywhere to be seen save for a small set of scrolls on Elder Rise in Thunder Bluff. Given that the Horde in general seems to lean more towards using violence to solve their conflicts, where do the tauren fit in, and why did they choose to sign up with the Horde in the first place?
The answer stretches all the way back to Warcraft III, when Warchief Thrall traveled to Kalimdor on the advice of the Prophet, a mysterious figure who would later be revealed as Medivh. After landing in Kalimdor, Thrall and his people found themselves in a much harsher land than the one they'd left, with new enemies like the centaur, a tribal race of primitive, bloodthirsty creatures, half-humanoid and half-horse in appearance. But Durotar was not without allies, as Thrall discovered when he happened across the tauren.
The tauren were originally nomads with no real "home" to speak of -- they simply traveled from place to place, living off the land in large groups or tribes. It is unknown as to how many of these different tribes actually exist, because of this nomadic nature. As they never really settled in any one particular place, the tauren were literally scattered all over the world, though the majority of them were concentrated in Kalimdor. Thrall came across a tauren who was under attack by the centaur and saved him, a tauren from the Bloodhoof tribe led by Chieftain Cairne Bloodhoof. Chieftain Cairne was both grateful for the rescue of his tribesman and intrigued by the nobility and savagery of the orcish race. He explained to the warchief why the Bloodhoof were traveling; while his people had been nomads for centuries, Chieftain Cairne wished to return to the verdant lands of Mulgore, the ancestral homeland of his people. Thrall spoke of the orcs and their flight to Kalimdor to find their destiny, and Cairne told him of an oracle to the north, offering to give him the location of the oracle in exchange for protection from the savage centaur on their journey to Mulgore. Thrall agreed, doubtless feeling no small connection to the chieftain and his wish to find a stable place in which his people could settle and thrive.