The Calamity Conjecture

What happened to cause the sudden disappearances of all the peoples within the Godsfall desert ? Excerpts from Pre-Calamity Godsfall by Rowan McCain suggest that there was a great conflict between two rising superpowers, one with grand magic the other with superior technology. One of the two factions crafted a weapon that must have gone totally astray and destroyed the entire region. With two notable exceptions include Greensward and Hafa. The first was spared by Erastil, for they did not prescribe to either faction within this war and should not punished for their actions. The second was spared for unknown reasons and by all accounts was uninhabited during the calamity. However the oasis is the only of it's kind for hundreds of miles.
There were two factions what were they like? Further readings from McCain's works suggest that prior to the Calamity these two nations worked together though grew independently. Meaning one prioritized the advancement of magic while the other delved into the sciences. They lived in harmony until just a few years prior there must have been some falling out between the two peoples.
What was the region like before the Calamity? While even fossil records have been completely buried by the desert that stands there now.  Some indication can be derived from the state of a forest that was sheltered from the blast by the Haji Mountains.  While it's not supposed the the whole land was wooded as just to the east of the Silverstream are vast plains, it is likely that the lands throughout were fertile and lush.