The Taunka are an interesting addition to the Horde Expedition forces. Discovered by Garrosh Hellscream shortly after his arrival in Northrend he is able to convince these ancestral cousins of the Tauren to assist them in their fight against not only the scourge but the Alliance as well. This is an astounding feat as the Taunka are already engaged in the task of grim survival against the elements and over all seem to be losing. Unlike their Tauren brethren the Taunka view the elements as something to bend to their will rather than a cooperative partnership, perhaps this is why Garrosh deals so well with them. Horde players will encounter them shortly after their arrival in Northrend as quests for this faction are located both in Howling Fjord and the Borean Tundra.
The exact origin of the Taunka is lost. There is some speculation that the Taunka could in fact be the Icemist Tauren, a fact further reinforced by the name of their capital Icemist Village. The Icemist Tauren were introduced back in the World of Warcraft Roleplaying Game and the similarities between the two are certainly there. Physically they resemble Bison more than Cattle along with having significantly lighter coloration than the Tauren.
While technically the Taunka have six villages in Northrend players will quickly discover that the vast majority of them are being evacuated or abandoned as the Taunka are finding themselves overwhelmed. Icemist Village has been completely overrun and destroyed by Nerubians leaving the Taunka without their main home. Taunka'le Village is being evacuated in anticipation of a scourge attack. Camp Winterhoof is planning to evacuate. Camp Oneqwah, a place many Taunka are fleeing to as a refuge is dealing with neighboring humans who are actually Worgen. This leaves really only Westwind Refuge and Camp Tunka'lo as safe havens.
While Garrosh may have thought gaining the Taunka to his cause would be a way to strengthen his armies in actuality it in fact is bringing THEM more benefit and saving THEM as a people from extinction. It may not have been intentional but Garrosh has become a hero to this people by bringing the Horde to their aid and perhaps this will aid him as nothing else in his raise as leader by saving these cousins to the Tauren.
Before Patch 3.3 you would cap out at Honored with this faction after doing all of the 79 quests available for them. Since that patch you can now gain reputation with them as a Horde player by doing level 80 dungeons while not wearing a reputation granting tabard as well as by doing the Champion level quests for the Argent Tournament.