For all of its strength, and its ability to conquer human adversaries, the Kaselreich has a disease, and that disease is known as The Schwarzvald. The Schwarzvald is an affliction unique to the Reich that develops in old forests at certain times. It can be contained at times, suppressed at others, but it can never be truly destroyed or eliminated. It is a perpetual presence in the Reich’s endless woodlands, a threat that hinders the Reich in projecting its power outside of its borders. Even the old rivals of the Kamens, the Gallians, have noticed that the Reich can never focus more than a fragment of its power upon them at a time, no matter their transgressions against it.
A Schwarzvald, or "Black Forest" can occur under many conditions. A forest that sees an unusual amount of death, disease, suffering, strife, or famine (all very common in a state that is constantly at war with itself) can become a Schwarzvald, as can one where the people live in terror for too long. Religious presence helps to repel the Schwarzvald in the immediate area, but causes it to intensify outside, like shadows darkening at the edge of torchlight. As well, the influence of dark magics, such as those practiced by witches, can hasten the coming of the Schwarzvald, though it is beyond their power to initiate the event.
When the Schwarzvald forms, dark forces begin to work in the depths of the woods. Trees gnarl, underbrush thickens, gentle beasts turn vicious, and dark creatures from ancient times emerge from their hidden places. Black Goblins, Nachtmachers, Rottreiters, and things too terrible to have names gather in the Schwarzvald as it forms, and begin to plague the surrounding countryside.
Townships embroiled in the Schwarzvald begin to change. The people become moody, paranoid, and at times bipolar. Many townships are gripped by hysteria, blaming their declining fortunes on their own people. Witch hunts are common, and sometimes these help — particularly if there are in fact actual witches, and they are actually hunted — but more often only serves to hasten the descent into madness.
Inevitably, the killings begin, as the dark forces that surround the village begin to creep in. At first it occurs at night, drunkards, beggars, lepers, thieves, but eventually families in outlying homes vanish, dark shapes can be seen watching from the treeline. Strange signs and fetishes appear over doorways, marking wells, and etched into stable doors.
Larger cities usually pull together and through sheer numbers cleanse the forests with fire and sword. Smaller villages are not always so lucky. Many are overrun in a single night of slaughter, man women and children all dragged off into the forests to unspeakable fates at the hands of creatures wicked and cruel beyond imagining. Others mount desperate last stands, and survive, surrounded by corpses that fade and vanish in the coming dawn.
Whatever the horror, the Schwarzvald is never permanent. It vanishes when its force is spent, and slips back into hiding, waiting for a new gate through which to enter the Reich’s forgotten corners and prey upon its people.
Thusfar, the Schwarzvald has never appeared outside of the Kaselreich, but at one time it had never been seen outside of the central province of Kamenia. Then it spread to Sezonia, then Kavaria, and beyond. Now it has begun to creep into the outer provinces, almost as though pursuing the borders of the empire.
Some suspect that it is a curse placed on the House of Kasel, a mystic vendetta set upon the Imperial Family by forces unknown. In Galli, it is popularly thought to be a divine punishment for the assassination of Clovis the Great by (they claim) Kamen agitators. In the Reich, this is often spun the other way, with the Schwarzvald being a curse that can only be lifted by avenging Clovis's assassination by Gallians.
The official Ruvian position is that the Schwarzvald is proof of the divine nature of industry. More forests should be clear-cut and replaced with good farmland and industry in the name of Indefatigable Genosus. There can't be a Schwarzvald if there's no vald to begin with.
At base, the Schwarzvald's most common threat is itself, and the wildlife that occupies it. These are not monsters, per se, but rather the corrupted elements of the forest that have become part of the Schwarzvald.
Wolves become darker, more aggressive, ravenous, and they lose their taste for the flesh of deer and sheep, and gain a thirst for human blood. As they feast, they grow larger, and their eyes begin to glow. There does not seem to be any upper limit to this. In a particularly harsh Schwarzvald, packs of wolves may be led by an alpha the size of a bear.
Trees become crooked, and begin to move on their own. Their branches gnarl and twist, blocking off paths, creating a maze-like environment that is difficult to penetrate even with the aid of axes, swords and fire. The thorny underbrush seems to curl around the legs of anything that passes through.
Deer are considered by most to be some of the most dangerous. Stags tainted by the Schwarzvald begin to move and think as one, and prowl the forests in formation, looking for men. When they find them, they emit horrific human-like shrieks that draw the attention of other, more predatory denizens. These twisted deer do not partake in the slaughter, but they gain a taste for flesh, and feast upon the dead after the predators have taken their fill.
Another common victim of the Schwarzvald are goblins. A great many of them occupy forest caves and shelters, and live in close enough proximity that when the forest is tainted, they are tainted as well. They become possessed by the same madness as the rest of the forest's creatures, a thirst for human blood and a desire to encroach upon and ruin civilization. Many of them can be found prowling with tainted wolves, knives gleaming in the dark.
These are just the natives to forests changed by the Schwarzvald, and they are by no means the most terrible of creatures.
When the Schwarzvald grows too powerful, too out of control, its animal population inevitably perishes or migrates in search of sustenance. In the dark heart of the black forest, only those things native to the sick, lifeless environment remain.