The rich drained the world of its resources, and when the world woke up to what was happening, they chose to build dungeons and fortresses to hide away rather than face the consequences of their greed. The centuries have worn down these once-impervious strongholds, and the desperate inhabitants of the barren world are more desperate than ever to breach these strongholds and claim the resources inside for themselves.
This is a companion discussion topic for the original entry at https://rpg-trader.com/products/4603/perils-and-parasites