The Feudal world of Karach had a culture and technology level akin to that of Early-Modern period Britannia on old Terra.
The aristocracy of the planet ruled with extreme decadence, allowing their peasantry to live in abject poverty while they themselves lived in beautiful estates and ate luxurious imports from the southern continents.
The Aristocracy spent their time primarily with sport, particularly the sport of hunting.
While most merely hunted the harmless but clever groundmink or the endearingly stupid Karntalope, the proud and the mighty hunted the great beasts of the south.

When the powers of chaos stole Balthasar from the Emperor of Mankind, his long journey through the warp came to an end on Karach.
His small pod crashed into the estates of Lord Bornhold, most powerful of the aristocratic lords.
Lord Bornhold, lacking a male heir, secretly claimed Balthasar as his own kin, grooming him for command and luxury.
Balthasar quickly took to the hunting sports of his father, and became renowned among his peers as the greatest huntsman on the planet.
Often on his expeditions on the southern continent, even his native guides would balk at his deep journeys into the jungle, and his tendency to use melee weapons rather than safer firearms or traps.
Other Aristocrats alternately called Balthasar Bornhold brave, insane, terrifying, and dangerous.
However, even his greatest detractors found him to be a jolly, friendly man whom it was exceedingly difficult to hate.
In truth, Balthasar was an inherently violent man with an terrible bloodlust. Only through his hunts was he able to sate his dark desires, desires he was deeply ashamed of.

One day, as he traveled back to his father's estate from an afternoon's hunt in the woodlands, Balthasar came upon one of the peasant villages which owed fealty to his father.
He had never visited such villages before, having been taught that peasants were dirty, feral, and barely human.
On the contrary, he found the peasants to be welcoming and friendly, though he could see the exhaustion and fear hidden in their eyes.
Over the next few weeks he met with the peasants in secret, and they told him many things which his father had kept from him.
Coming to consider the peasants a truly noble underclass, it did not take long for Balthasar to see the oppression and injustice of aristocratic rule.
Balthasar trained the peasants in the ways of war, and lead them in revolution against his father to seize the means of production.
Originally planning to kill as little as nessecary, the revolution quickly reached a tipping point.
Hunting parties scoured the cities, pulling pampered women and pompous men from their homes and killing them in the streets.
The peasants even took scalps and pelts from their former overlords, wearing them as trophies.
The revolution began eating itself the moment Balthasar gave the commoners power and he realized that in the end everyone simply wanted the oppurtunity to spill blood.
Because of this, Balthasar realized that cruelty and violence are the only thing universal.
Relieved to know he was not the only one to possess this bloodlust, he only became happier. He knew he was not alone.
Eventually Balthasar killed his false father himself, skinning him alive.

The Emperor came to Karach soon afterword. The Emperor came under the guise of an envoy, offering to welcome Karach into Imperial compliance peacefully.
Having just thrown off bourgeois oppression the people of Karach were hesitant.
Balthasar's keen mind, however, saw to the truth of things: his people could never defeat the soldiers of the Emperor.
He proposed a contest of skill. Balthasar and the Emperor would hunt the southern jungles for Jumaal, a shadowbeast which had eluded Balthasar all his life.
For five weeks, the Emperor and Balthasar scoured the jungle for tracks, scents, and trailsigns. Finally, Balthasar found Jumaal in the highlands at the center of the continent.
Jumaal was a catbeast with a pelt of dagger-like black quills, each one capable of spearing a man to death. Balthasar wrestled with the beast for ten days, until the Emperor came upon them.
Seeing that his son was slowly losing to the beast's poison, the Emperor stepped in and struck down Jumaal.
Balthasar was grateful, and the Emperor chose that moment to reveal to his son the truth of his nature and origins.
A cloak was made from the quills of Jubaal, and the Primarch wears it even to this day.

Balthasar's revolution had thrown the nations of Karach into disarray. By the time of the Emperor's arrival, he was attempting to maintain some semblance of control over the proletariat uprising.
By this time, he was cracking down with the same bloody measures used by the aristocrats before and the violence seemed never ending.
After swearing fealty to his father, Balthasar was brought to Terra to be taught the ways of the Imperium. The first legion, now renamed the Bloodhounds, forcefully brought the Pax Imperialis to Karach.