You can actually read a summary of the story, as well as a fully written out History-Past-Current synopsis on the official Antreyan website. It explains what happened that caused the Antreyan world to fall victim to a nigh apocalypse and how they are starting to rebuild civilization.
Rebuilding a civilization from near extinction means they would have prior knowledge of how life was once and so they could make intricate items (Steampunk), but they would be living in a world that still has a lot of work to do before it is fully back to a civilization (Medieval).
AntreyaOnline
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Antreya Chronicles Online is a Mystical Fantasy and Steampunk, post-apocalyptic MMORPG in the world of Antreya with Live Storytelling.