Throughout the city, the Plague was going on. It traveled to person to person from filthy rats that had fleas that sucked the rats blood than hopped to humans and puked the rats blood into the humans blood stream and gave them the plague.
The Plague hit hard on the population at the time, it killed 2/3 of the population. 75-100 million total people. It took 300 years to recover.
The Serfs started demanding money because how hard they are working and how there is limited serfs throughout the city to work for the King.