Fingers can be pointed here at draenei complacency, although to me that's a touch unfair. Still, it can't be denied that after thousands upon thousands of years of running from demonic maniacs who used to be their friends and neighbors, the draenei as a whole just wanted to have a place to call their own. They didn't react as quickly to the orcs and their sudden bellicose stand as they could have: having once hosted a young Durotan and Orgrim Doomhammer, Velen was under the impression that the up and coming orc leadership was admirable and could be negotiated with. Unfortunately he failed to grasp the true extent of the hostility that Kil'jaeden had created, nor did he know its ultimate source. Had he seen the hand of his old enemy, it might not have mattered, for with K'ure entombed within Oshu'gun the draenei lacked a ready means of escape. Velen made the mistake of attempting to visit K'ure's resting place at this time, which only agitated the orcs further (and led with the Prophet being briefly held captive by the Frostwolf chieftain Durotan, who held Nagrand at that time).
The fall of Ner'zhul and the rise of Gul'dan ended any chance for peace between orc and draenei, and Durotan's betrayal of the means by which draenei had brought him and Doomhammer into Telmor sealed that city's fate, as demon blood addicted orcs slaughtered the inhabitants. While the draenei did not go quietly... their mastery of arcane power, the Holy Light first shown to them by the Naaru, and natural size and strength allowed them to fight effectively and the orcish dependence on the spirits meant that as they took actions the spirits disapproved of, their power waned.... Gul'dan quickly set about replacing waning shamanistic power with warlock magics that the draenei were not equipped to resist en masse. Eventually, even Shattrath City fell. Gul'dan set up camp in the former Temple of Karabor, Velen's own private sancturary, and transformed it into the Black Temple.
This unchecked, unjustified, and rapacious violence was the result of Kil'jaeden taking advantage of the aggressive hunter mentality of the orcs and magnifying it first with paranoid and suspicion and later with demon blood taken from an Annihilan, Mannoroth. While these elements were already present (hey, you try fending off ogres and gronn with good looks, it takes some significant whacking with big, heavy objects to keep those dudes off your back) it was the culmination of Gul'dan's manipulation that convinced so many to willingly enslave themselves to demons. The complete slaughter, the genocide waged upon the draenei was Kil'jaeden's goal, but it was an afterthought to Gul'dan, something he engaged in merely to cement his own power.
As the orcs fell to squabbling and Draenor, poisoned by fel corruption, began to become unlivable, the few remaining draenei gathered together in hidden refuges placed in regions no one would really want like Zangarmarsh. Velen had been forced to allow himself to be protected and removed from the major centers of draenei life as they fell, forced to watch as his followers were slaughtered in vast amounts. Now some of the draenei were finding themselves changed by the fel energies unleashed by heedless orc warlocks.
Unfortunately, the draenei did not respond to this new problem with the equanimity one might hope for. Already reeling from the carnage of the orcish assaults, many draenei responded to these 'broken' with horror and revulsion and ostracized them from their already reduced society. These unfortunates were named 'krokul', or Broken and were often forced to become hermits... when and if entire tribes were not so stricken. Akama, formerly a priest at the Temple of Karabor, ended up leading an entire tribe of broken.
In their reduced state it would have been fairly easy for Gul'dan to have finished the job, but as was stated above, he didn't really care about the draenei at all: it was Kil'jaeden that had wanted revenge, and he withdrew his influence, sated at having forced Velen to watch his people die by the myriad myriads. (Yes, I reference Procopius.) Gul'dan found himself much more interested in finding a way to keep his people alive, which not only led to his alliance with Medivh/Sargeras and the opening of the Dark Portal, but gave the remnants of the draenei breathing room. (It also allowed Lost Ones, a tribe of broken further mutated by fel energies, to make their way to Azeroth. To this day Lost Ones can be found in the Swamp of Sorrows and Blasted Lands.)
Velen and his followers hid at the former anchorage of Telredor, and Akama lead his Ashtongue tribe of broken. The former Vindicator Nobundo walked the land attempting to reconnect with the Holy Light that he had lost when he was one of the few survivors of the massacre at Shattrath. Then Ner'zhul tore Draenor apart, and created Outland, the shattered ruin of the once lush planet. In the aftermath of his action the draenei actually seemed to recover somewhat, as not only did the orcs have more pressing matters (like pure survival) to occupy them, but the Naaru of the Shat'tar faction arrived at Draenor in what would be known as Tempest Keep as well, to try and lead resistance to the Burning Legion. Together with the Aldor, they helped reclaim and rebuild Shattrath from the charnel pit the Horde left behind.
The coming of Illidan to Outland brought change that aided and yet also harmed the draenei. Akama and his tribe of broken allied with Illidan and helped him close the portals and reclaim the Black Temple (formerly the Temple of Karabor) from the pit lord Magtheridon but Illidan's ally Kael'thas Sunstrider led a force of blood elves to seize control of Tempest Keep while the Naaru were occupied helping the Aldor at Shattrath, seizing M'uru in the process. This led Velen to determine that the time was at hand to leave Outland once and for all. With Nobundo having returned to Telredor and demonstrated that the draenei affinity for magic extended itself to the elemental and ancestral spirits of the land that the orcs had abandoned to chase after fel magic, Velen began to believe in the words of an old prophecy of his and took direct action for the first time in decades. A force of draenei and broken stormed Tempest Keep, managed to commandeer one of the four satellite structures, and escaped Outland, although not without sabotage from the blood elves loyal to Kael'thas.
A starting draenei PC picks up his story from this point: the Exodar, the crashed satellite of the Naaru dimensional fortress sabotaged by Kael'thas' servants, has ripped a hole in the Twisting Nether and arrived on Azeroth, crashing into islands loosely controlled by the Kaldorei. A starting player gets to experience the aftermath, as injuries are tended to, the new world is explored, contact is made with the Alliance and eventually a great threat is dealt with, earning the respect of the draenei people.
The draenei, led by Velen, provide the Alliance with their real foothold back into Outland, while Nobundo's teaching allows the draenei to tap into the same spirit magic as their enemies in the Horde. It seems that the draenei are in an expansionist phase now, as their presence can be felt in settlements in Ashenvale, in ambassadors sent to Stormwind and Aerie Peak, and even in Northrend where they work to root out corruption. They're done running. Velen took part in the final banishment of Kil'jaeden and the restoration of M'uru, and in so doing re-created the Sunwell, proving that the draenei can do good even to those who have only offered evil to them. Survivors who have touched the Holy Light, heard the spirit's call from their desertion and answered, and worked magic unlike any people before them have joined with allies to ensure that what happened on Draenor will not happen to Azeroth.
Basically, draenei are awesome. Next week, most likely we'll talk about Velen and maybe Nobundo as well.