In the time before the Arrival, small kingdoms laid siege to each other in violent wars, pitting rams and catapults against castles and the lines of horseback soldiers that defended them. Their acts of factional destruction kept them divided, focused on piety and allegiance rather than what they could accomplish together.
Earth forever changed when massive spacecraft appeared over the planet, and descended from the sky. Initially a malfunction of one of the craft brought it crashing down, the now broken capital carrier ship being scavenged irregularly by opportunistic outcasts of the human kingdoms.
The support ships that were accompanying the mother-ship remain in operation, however. They periodically abduct humans to examine their physiology, and genetically modify themselves to adapt to Earth’s biosphere. Some of these humans bargain for their survival, swearing loyalty to new alien masters, selling out old alliances for technological power at least 5,000 years too advanced for them.
The aliens themselves are biological beings, despite their use of mechanical technology to traverse the stars. To defend their crashed mother-ship and its technological resources, alien horrors are unleashed upon humanity. The human kingdoms view these aliens variably as gods, devils, or just another faction to ally itself with or against. The aliens see humanity as slightly sophisticated animals, usually only fit for experimentation, biomass fuel, domestication, or sport hunting.
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