The Calamity

In the days of The Astrals, magical research and technology was at an all-time high. They dominated the elements with their floating cities, called upon the powers of the gods with their churches, and created new species and creatures with their druidism. However, there was one kind of magic they had never dared tried: Inter-planar Travel.

The Nexus Gateway
With their infinite magical knowledge, the Astrals had come to learn of The Soul-Nexus, a "river" which transported souls into their respective afterlives. Curious about this power, they constructed a gate to access it, hoping they could learn to navigate it and learn more about the other planes in the process.

The Nexus Gateway was massive, and was housed on a large floating island somewhere in the southern hemisphere. To power such a large device, they needed a power source stronger than anything they had at the time.

The Bargain
Clueless about how to power the Gateway, the Astrals researched tirelessly to find a viable method. After months with no result, A young mage was granted a vision of Acherus' impressive soul magic by Illdaeron, who offered him a deal. Illdaeron would provide the power necessary to power The Nexus Gateway, provided he could use it as a method of bringing his demonic armies to Last Bastion.

With little knowledge of the Demons and how dangerous they were, the young mage took this Faustian bargain and brought the power of soul magic before the other Astrals. Astonished, they began work, and within the year, the Gateway was ready to open.

The Betrayal
It was a monumentous occasion the day the Gateway was to be opened, with a world-wide celebration. The young mage was given the honor of turning on the machine, and he did so to ravenous applause. As the Gateway opened, however, it's silver hue turned a deep blue as Demons began to rain from it, bringing destruction wherever they went. Illdaeron had lied, and used the Gateway as a means of entering Sillania.

In a matter of weeks, the Astral civilization was completely decimated, and Demons ruled the world.

The Aftermath
What happened next is not quite known, however historians believe that the Gods intervened eventually, sending The Valarien to conquer the demonic threat. With the Gateway destroyed and all forms of civilization gone, the world of Sillania was nothing more than a barren husk of what it once was. As the years went on, however, the corruption naturally subsided, and new races of mortals came to take the place of The Astrals, ushering a new age of Post Calamity growth.