The Primum Crisis was an internal conflict in the City-State of Uthan between the Mayor King Leontine Shanasa and the various magnates and trade leaders of Uthan.
The Shanasa family had long ruled Uthan as the Mayor Kings of the City-State, a position borne from the political maneuvering of Munadra in the aftermath of the ousting of the former governor of Uthan in a coup. During his rule, he had consolidated support within the government and formed alliances between the Shanasa and other powerful trade families, as well as helping to deepen the divide between other magnates in order to ensure that another coalition couldn't rise up and overthrow him.
By the time Leontine rose to the throne, it had been nearly two centuries since Munadra had consolidated the Shanasa family as the de facto rulers of Uthan. With a lion's share of the spoils brought by the taxes and benefits that came with being the center of the world's trade, Leontine grew up with a golden spoon in his mouth, without much of the necessary teaching of the political landscape of Uthan. As a result, he held a simplistic view of the different relations inside Uthan and of the economic policies that were in place.
Since his coronation, Leontine had begun to clash with the different magnates that made up Uthan's elite, alienating them diplomatically and certainly not making himself any allies. Many saw Leontine as a spoiled child given reign to one of the more powerful positions in the world, while others saw him as a dangerous fool that would drive Uthan into the ground with his decisions and policies. The new Mayor King also had no one to guide him on decisions of state or economy, his mother had died while he was young, he was an only child, and his father had passed away, leaving him the title of Mayor King and head of the Shanasa family. His political advisors were of those Leontine hade made friends with, giving the positions of power in exchange for relatively nothing. These friends of Leontine were often not experienced in forms of politics, or weren't part of the intellectual elite at all, meaning that they were mostly incompetent in their jobs, if not outright corrupt.
Leontine had also managed to poison his reputation among the common folk and the intellectuals of Uthan, displeasing the former by provoking multiple confrontations with those respected within local communities and wise local elders during many of his drunken escapades before and after his cnation, and angering the latter by diminishing the importance of the academia through a number of speeches and legislation passed. Even the army wasn't on Leontine's side, with the Mayor King having increasingly relegated more and more resources to different mercenary companies that were owned or related to the Shanasa family.
The final straw for Uthani magnates was the attempted assassination of Irnik Welensworth, one of the more vocal opposition to the policies of the Mayor King. The attempt, though a failure, was the tipping point for many. It confirmed suspicions that Leontine was actively against them, and gave purchase to fears that other members of those opposing Leontine would be targeted by assassins next. What followed next was the beginning of a second coalition of many different traders, important magnates, notable academics, nearly anyone who was important or notable banded together against Leontine, meeting in private buildings.
This new coalition wasn't very secretive either, and Leontine, a week after its banding together learned of it. He ordered the army and his mercenaries to hunt down and arrest those who plotted against him. The army largely didn't do any of this, seeing as a number of their commanders were in on the plot, and those that weren't didn't exactly feel inclined to do anything for the Mayor King so just sent him false positives and fake statistics while doing largely nothing. The mercenary companies, while a degree loyal to Leontine, realized that arresting basically anyone who was important (and who had no doubt mercenaries and private guards of their own) was an impossible or otherwise extremely costly endeavor, so did little, just reassuring the Mayor King and doing the same thing as the army.
The goal of the plotters was a topic of heavy debate. As a consequence of being composed of a great number of different people with their own beliefs on how the state should be run, no one could quite agree on what exactly to do. Some wanted things the way it always was, except with Leontine off the throne. Others wanted to try out the new "democracy" idea being espoused in Valdar. A few just wanted power for themselves. In the end, it was decided on a compromise, that the Mayor King would be kept on the throne (albeit with heavily diminished powers) and a Senate made up of important Uthani families to keep the Mayor King in check as well as for the Senators to exercise their power.
The plotters, however, also faced a great difficulty when coming up with the plot. They wanted a quick coup, in and out, Leontine arrrested within the day. If that failed, or Leontine escaped before and established a rival government, then a civil war might ensue. The plotters would win, no doubt, but the damage would be done. Every single nation that bordered them would literally jump at the chance to take a slice of the valuable pie of Uthan, fighting with themselves and the plotters over the territory and basically carving up Uthan with a knife. The desired outcome was a quick deposition of Leontine before word escaped about what was happening.
On the Ninth of Primum, 303, multiple groups of Uthani Army soldiers stormed the palace, resulting in several small skirmishes with loyal mercenary groups. A majority of the mercenaries loyal to Leontine simply stood to the side or surrendered when faced with fighting for a King they really didn't like or trust to keep payments on time, most just didn't fight. The fighting didn't take long, and before Leontine could flee the palace, he was captured by the soldiers, preventing the worst case scenario of a civil war in Uthan.
The plotters, now the dominant authority in Uthan, declared that Leontine was unfit to lead, deposed him in favor of a minor cousin that was in the Shanasa family who was much more agreeable. The new Mayor King enacted every single reform that the plotters suggested, creating a new Senate and undermining his own power. With that, the group of plotters, who were only really kept together by their shared hatred of Leontine, fell apart quickly, leading to a more regular state of affairs. Leontine himself would later be assassinated, probably by a group that didn't want him sticking around and potentially making a comeback.