Ukari on Yathrib
The Ukari's history on Yathrib dates back almost as far as the planet's history, and largely their presence has been unwanted by the human settlers of the world.
While some Second Republic scholars suggest that there is evidence for Ukari settlement on Yathrib before human arrival, the first definitive contact came during the Ukar Wars -- the "forty years of night" where the Ukari occupied Yathrib, outlawing the Church and enslaving the settler population. While estimates are difficult to come by from such an ancient time, what scattered history remains suggests that the Ukari occupation force was quite substantial; Aylon is close by, and there are also references to Yathrib being used as a staging point for fleets from Ustar preparing to raid into the Known Worlds.
Finally, St. Palamedes led an army to Yathrib; while he departed, his army waged a ten-year campaign to cleanse the Holy World of Ukari. At St. Palamedes' order, most Ukari communities were put to the sword, while those Ukari who instead converted were deported from Yathrib and resettled on Kordeth and Aylon.
In the centuries that followed, Ukari were extremely unwelcome on Yathrib. Ur-Ukar travelers were often attacked, and when Ukari villages were found that survived the pogroms they were often killed outright or exiled from the planet. As a consequence, Yathrib developed an black reputation among the Ukar, who began to call it Mastar, the 'evil place.'
The liberalization of the Second Republic made Yathrib at least a little more open to the Ukari, as hate crime legislation prohibited the kind of direct attacks that dominated Yathrib's history up until then. Ukari were still not particularly welcome, at least among the long-time residents of the world, but colonies were established, particularly in areas where the al-Malik had a great deal of influence. Ironically, the largest colony was in Revelation itself, where an Ukari underclass that lived in the Alien Ward was established.
Despite Second Republic laws, there was still a great deal of antipathy towards the Ur-Ukar. Employment and housing discrimination kept them from flourish on-world, and Ukari-run starships transiting through Yathrib space had a separate space station from that used by pilgrims. When the Fall came, old tensions flared up even worse, as many of the Ukari colonies were set upon by pilgrims; most of those that survived fled to the Alien Ward, which became a ghetto for surviving aliens.
New Dark Ages
Very few Ukari colonies survived the Fall. The al-Malik, sensing where the wind was blowing, withdrew their protection from most of the Ukari colonies, though a handful of Ukari families survived in the Antipodes as direct retainers to rural al-Malik lords. In the early years, these Ukari retainers were kept very private, but they became more common fixtures within the last several hundred years.
Elsewhere, colonies were often burned out when found, and indeed it is widely thought that no independent Ukari communities survived on Yathrib after about 4200, though rumors of isolated outposts have popped up from time to time. Instead, surviving Ukari have either been integrated parts of al-Malik retinues or survived in the Alien Ward.
The Alien Ward survived despite itself. Over the centuries, it was subject to several pogroms, but underground tunnels provided shelter for Ukari to retreat to when threatened by overzealous Church officials. More than that, the Ukari had galisp farms in those tunnels, and so the Alien Ward was one of the only places where Revelation could produce its own food. While the Ukari weren't the only alien species in the Ward -- there was a large Obun and Hironem population as well -- they became particularly dominant in the face of human aggression, particularly because interbreeding between Ukar and Obun was very common in the Ward.
After the Kurgans conquered the city, the aliens were not subject to the Peace at the River of Joy; they were unwelcome in the refugee camps, and so they were just left in the Alien Ward, where they defend it against both the Kurgans and the Known Worlders while living in constant fear of bombings and collateral damage from the war raging over the city.
Since recontact, more Ukari have arrived on world. Al-Malik crusaders have brought elements of the Fifth Dark Legion to the Antipodes, while Ukari guilders have come in search of profit and adventure. Their reception in Akko, particularly, is very cool, but rumor has it that the Rebel Clans have been reaching out to the Ukari in the Alien Ward, trying to forge alliances. While the Ur-Ukar of the Ward have largely abandoned the cultural traditions of Kordeth, they share with the Rebel Clans a deep dislike for humankind, and the Rebel Clans in turn still smart from the pogroms that occurred on Yathrib after the Ukar Wars and in the intervening centuries.