Ambrosia is the secret behind the Hymbrans' golden age. It is a sweet smelling, viscous, golden liquid that can cure any ailment and nourish a person for several days. Although ambrosia was initially only available to the royalty and nobility, after only a few years enough was produced to be made available to everyone in the small nation. The king of Hymbra decided not to share his boon; he closed the borders and attempted to keep ambrosia within them.
The effects of ambrosia kicked off Hymbra's recent short-lived golden age - everyone was permanently hale and healthy and living to old age - leading Hymbra to become much more efficient. In this golden age, there were no mundane concerns of health or food, which allowed the Hymbrans to pursue their passions. The arts boomed and Gulham was remade a city of beautifully ornate marble; houses were filled with paintings, statues, and decorative furniture; and beautiful gardens were cultivated in both private and public places. Science also jumped ahead far beyond anything else in Morgrave: simple gunpowder weapons, compasses, improved furnaces, printing presses, and more were all created by geniuses who could spend all their time on their studies. Finally and most importantly, arcane magic was discovered. Previously, despite accusations of witchcraft in rural villages, divine magic had been the only type of magic on Morgrave. A university of arcane magic, the first of its kind, was founded in the mountains of eastern Hymbra.
After the discovery of Ambrosia, things that were usually under the purview of the gods, such as healing, became achievable by mere mortals, and with even better results. Clerics no longer had such a high distinction in the once religious Hymbra - people were turning away from the gods in droves because all their necessities were met by ambrosia. Soon enough, the gods stopped granting divine magic to the Hymbrans. Eventually their most devout disciples died and those who took up the mantle of priesthood found no answer for their prayers. This disappearance of the gods, which is still ongoing today, is called the Silence.
However, depending on how you define what makes a cleric a cleric, clerics haven't completely disappeared from Hymbra. Recently, the devout have used ambrosia itself as a catalyst to channel divine magic. These new age clerics believe that the gods did not abandon them willingly, because they are still clearly granting their divine magic. Others believe that the gods left as punishment for turning away from them. This claim is evinced by the other nations still having access to divine magic without the use of ambrosia as a catalyst, and also by the fact that Hymbrans are transforming into monsters - if that's not a curse by the gods, what is?