The trolls of Warcraft have a history that spans back further than any other playable race currently in the game, with the exception of the draenei. This makes it difficult to trace the entirety of their history, but fortunately the Darkspear of the Horde are one small fraction of what is a gigantic race as a whole. While the orcs, blood elves, Forsaken and tauren are all dealing with their own issues, the trolls of the Darkspear tribe are working quietly and largely by themselves to deal with a few major problems of their own.
The troll races of Warcraft were originally largely part of two major empires -- the Gurubashi of southeastern Kalimdor, and the Amani in the middle regions of the continent. There were other tribes scattered here and there, notably the trolls of Gundrak to the north, but by and large, all troll tribes fell under either the Gurubashi or the Amani empires. Prior to the Sundering, the trolls comprised a gigantic portion of the world's population, and while the Gurubashi and Amani didn't really like each other, they rarely warred, instead choosing to fight against a third empire, that of the Aqir. The two races fought relentlessly for thousands of years, and eventually the Aqir Empire split into two city-states, Azjol-Nerub to the north, and Ahn'Qiraj to the south. With the Aqir driven into exile, the trolls returned to their normal lives, though neither empire expanded much further than their original boundaries.
The night elves were now the ruling "empire" of the Kalimdor continent, but their reign was short-lived. Though their power and magical prowess was great, it had attracted the attention of the Burning Legion, sparking the events in the War of the Ancients and ultimately causing the Sundering that literally shattered Kalimdor. After the Sundering, the troll empires found themselves forcibly split across the newly formed continents. While the Amani Empire stayed to the northern regions of the eastern kingdoms and by and large managed to keep in one piece, the Gurubashi of the south dissolved. Fractured through no doing of their own, the Gurubashi Empire continued to splinter among the jungles of Stranglethorn Vale and the deserts of Tanaris.
Meanwhile, the Gurubashi Empire splintered even further. Civil war broke out amongst the jungle tribes, including one small tribe known as the Darkspear. The Darkspear soon found themselves pushed out of the jungle they once called home, forced to take up residence on what is believed to be the Broken Isles, where they continued to live for many years in their own trollish way. Keep in mind, the "trollish way" is that of a cunning, ruthless savage. The Darkspear were the smallest of the jungle trolls but also some of the smartest. However, the troll race as a whole was a violent one, prone to war and conflict. Most troll tribes practiced ritual sacrifice and cannibalism as well as black magic and voodoo arts, and the Darkspear were no exception to this at the time.
The Darkspear, along with some other troll tribes, believe the spirits of the world to be much like any living creature. The spirits can be greedy, hostile and dangerous, as well as sometimes benevolent and forgiving. The trolls tend to believe that their ancestors linger on after they've died as jealous spirits that miss the land of the living, spirits that require blood sacrifices to appease them. Cannibalism is almost a ritual to them as well -- by devouring the flesh of their enemies, they are also devouring their enemy's spirit, preventing it from returning later for revenge. The Darkspear followed these beliefs along with all the jungle tribes out there on the Broken Isles they called home, until somewhat recently.
A dark creature known as the Sea Witch was responsible for the murlocs' sudden change. The Sea Witch was a goddess who the murlocs worshiped, an undead naga banshee who had taken over the Broken Isles. Powerful and ruthless, she demanded daily ritual sacrifices from the murlocs of the isles, resulting in their attacks on the Darkspear Tribe. Sen'jin and the Darkspear were now being attacked on two fronts, the humans of Kul Tiras and the murlocs of the Sea Witch threatening to decimate them. One night, Sen'jin received a vision from the spirits: a vision of a young orc, a farseer who would drive the humans away and lead the Darkspear from the island and to a new destiny.
Shortly after this vision, yet another group visited the Broken Isles -- this time, Thrall's forces that were on the way to Kalimdor to seek their destiny at the behest of the Prophet. Thrall and his Horde had stolen ships from the Kul Tiras to make their way to Kalimdor, but underestimated the force of the Maelstrom that nearly destroyed the ships. Forced to take refuge on the Broken Isles and repair the broken ships, Thrall was approached by Sen'jin, who warned him of the human settlements nearby. Thrall, having dealt with the humans extensively over on the Eastern Kingdoms, agreed. He wasn't terribly fond of the human population in general at this point, and Sen'jin seemed agreeable enough, even leaving some of his people to help Thrall out.
This all took place in the introductory campaign for Warcraft III, and while Thrall and his forces succeeded in pushing back the human forces, they were captured shortly after by a band of murlocs. Thrall, Sen'jin and a host of orcs and trolls were taken underground to be sacrificed to the great Sea Witch. While Thrall managed to free himself and several other imprisoned orcs and trolls, Sen'jin was taken to by the murloc high sorcerer into the deepest part of the lair to be sacrificed. Thrall and his combined forces battled their way through the murlocs to reach Sen'jin, but they were too late -- Sen'jin was dying. With his last breath, he told Thrall of the vision and begged him to take the Darkspear from the island and save them from destruction.
The Sea Witch was enraged, furious at the defilement of her sanctuary and the slaughter of her minions. She summoned powerful storms and waves to batter at the small islands, intent on destroying the orc who opposed her and the trolls that had been a thorn in her side. It looked as though the Darkspear of the Broken Isles would surely be destroyed.
Once they arrived in Durotar, Vol'jin and his tribe of Darkspear established a home for themselves on the Echo Isles (possibly named as such due to their resemblance to the Broken Isles, their former home) and created a settlement that was soon under attack. Once again, the Kul Tiras fleet found the Horde, and Grand Admiral Daelin Proudmoore's fleet attacked the trolls without mercy. Vol'jin and his people were saved yet again, this time by the efforts of the half-orc Rexxar, the shadow hunter Rokhan and Chen Stormsnout, a pandaren they'd picked up along the way. Forced to retreat from the Echo Isles, Vol'jin continued to help Rexxar and Rokhan, advising them to recruit the tauren and the ogres to help fight against the human forces.
After all was said and done and the Grand Admiral was taken care of, Vol'jin and his people moved back to the Echo Isles, this time to settle peacefully. Unfortunately, it seemed that peace was not in the cards for the Darkspear. The witch doctor Zalazane, formerly one of the trolls responsible for training young Darkspear priests and mages, was angered at the alliance with the Horde and enslaved many of the Darkspear on the island. Vol'jin and those remaining were forced to beat a hasty retreat. Once they reached the shores, the Darkspear established a small fishing village that was safe from the threat of Zalazane and named it after his father. Sen'jin Village is tiny, more of an outpost than a village and now led by Master Gadrin, one of Vol'jin's most trusted advisors. Gadrin is intent on seeking out Zalazane's end and recapturing the Echo Isles for the Darkspear once and for all. New Horde players will find themselves sent after Zalazane, as well as being asked to help combat the nearby centaur menace that is threatening the tiny village.