Of course, social progress is slow in any world, and some places have taken to undead acceptance faster than others. With few exceptions, liches are the earliest and mostly easily accepted in any society, followed by vampires, mummies, skeletal champions, and ghouls rarest of all. Large cities such as London, Berlin, New York City and Chicago tend to have entire undead districts or neighborhoods, while cities like Cleveland, Glasgow, or Dresden will have a score of notable undead personalities. Once you get to a place like Akron or Heidelberg, there are maybe three or five liches and vampires, and any city smaller than that is unlikely to have any undead at all. Indeed, outside of these large cities the presence of undead is rarely tolerated, or if it is it is only with a very begrudging and prejudiced attitude. None of this is helped, of course, by the roving bands of ghouls who hunt down travelers and caravans for food between wars, the vampire nobles who abuse their power in Eastern Europe, or the liches who care more for their magic and experiments than the lives of those around them.
Perhaps the most feared of all the undead, or at least, the most viscerally so, ghouls sustain themselves on the flesh of other sentient beings. They can survive on non-sentient flesh, but it is broadly described as flavorless - something akin to poorly prepared tofu. Those ghouls absolutely set on integrating themselves into mainstream society adopt this "vegetarian" diet, while many others resort to lives as soldiers, bandits, or hitmen to satisfy their cravings.
Ghouls are seemingly created by accident when a human is killed by a ghoul's bite, though it is difficult to predict if a particular victim will rise or not. This has led some researchers to wonder if ghouls, and perhaps even undead to a larger extent, are created by a contagious agent, some virus or bacteria.
Of all the undead races, liches integrate into society most easily. After all, feeding on magic - that's not so bad, right? That's not harming anyone mentally or physically. They can even feed on their own magic, making them even less of a threat. Of course, this is tempered somewhat by the high proportion of liches who are Collegium members (al Mushtamir and the Banister School also being common), and the rumors of... unsettling magical experiments performed by some liches.
Liches are created through a complex magical ritual, which must be performed by the person intending to ascend to lichdom. All attempts to transform with aid from others have failed catastrophically.
The rarest form of undead, mummies feed on fear itself. This puts them in a curious place relative to integrating into mortal society: they don't harm people, precisely, at least not bodily, but they are still deeply unpleasant to interact with. Generally speaking, this leaves mummies in the middle of the pack as far as integration goes, though their low population means they are still rarely encountered.
Mummies, like liches, are created through ritual, but the process of creating a mummy must be performed by others on the behalf of the mummy-to-be. The art was largely lost for many centuries, except perhaps in Collegium and al Mushtamir libraries, but new embalmers are being trained in this more permissive era.
Skeleton champions are unique amongst the undead in that they can arise entirely spontaneously from areas of intense conflict. Generally speaking, even the largest, most brutal battles will create only a handful, which are usually either destroyed by local authorities soon enough, or collapse due to a lack of conflict to sustain their forms. However, during the Great War, the trenches between France and Germany saw death and destruction the likes of which the world had never experienced before. There are entire swathes across this border which are infested with skeletal champions to the point that, even over 15 years later, no country has undertaken a serious, focused effort to destroy them. Perhaps if France and Germany cooperated, such a thing would be possible... but obviously, that will never happen. Fortunately, the skeletons do stay within a relatively consistent area, rarely venturing out, and mostly sustaining themselves by battling one another, occasionally including large-scale grisly re-enactments of trench warfare.
Skeletons thrive on the very strife that initially births them, limiting their options to integrate into larger society. The majority simply fall apart or become criminals of one sort or another to survive. Of those who do find "legitimate" work, most are mercenaries or bodyguards in high-risk areas, while some others find work as trainers in self-defense or even boxing. Interestingly, the conflict a skeleton needs to survive does not have to be lethal, so these positions can suit them quite well.
While a vampire's reliance on blood may seem to have hindered their potential integration, the fact that they do not require a victim's death to survive mitigates this greatly. That and, of course, the intense personal charm many vampires possess. Unlike other undead, vampires can easily pass as their previous race with only the smallest of concealments, another factor that puts mortals at ease.
Vampires operate in regionally-organized courts, which consist of a number of bloodlines. Heritage and geneaology is central to vampire culture worldwide, and whom one was turned by is an important mark of status. Vampire courts tend to operate independently of and parallel to human governments. Generally, vampires see themselves as above petty human nationalities and such. They may have a loyalty to a French culture or a Spanish culture, but when human governments rise and fall multiple times within a single vampire's lifetime, they care little for any particular country's interests (though they are happy to use human political conflicts for their own purposes, when it is possible). While the bloodlines within a court regularly fight and scheme amongst themselves, they tend to unite when faced with an outside threat - unless, of course, the outsiders can make a better offer. Free agent vampires exist in locations that are not of interest to the courts, but are rarely allowed to reside long-term in court-controlled territory.
Mortals are turned by drinking the blood of a vampire. Generally, it takes a handful of good swallows to successfully turn, making accidental vampires incredibly rare. Turning is excruciating and takes some time, requiring a safe place to finish the transformation (which also reduces the rate of accidental vampirism).
Vampires graduate from fledgling status when they gain Discorporation. At Entrancing Gaze, a Vampire gains the title of Master, and this is generally the level that the head of any individual vampire household is at. Vampire powers are effectively the same all around the world, though certain courts may train more often in certain other tracks.