It all starts with a volcanic eruption theorized to be located in Iceland. The dust and smoke went through Africa, Europe and Asia triggering a reverse greenhouse effect that would last 18 months. 

Without as much sunlight, agriculture became near impossible and mass starvation ensued. Also, the Northern Hemisphere saw severe cooling to the point where China saw snow in the summer. 

Also The Byzantine Empire was still at war with the Goths in Italy. Disease went rampant and caused many to “fall asleep forever.” It is obvious that the economy was in free fall during this whole year. The economy was hit so badly that it took a century to recover.