In AG (Advanced Generation) 101, space colony Angel was destroyed by a mysterious and incredibly advanced enemy force. The infamous attack, known as The Day the Angel Fell, marked the beginning of a long war against the Unknown Enemy, as the Earth Federation initially called it.
It wasn’t until after the initial battles that the Unknown Enemy turned out to be descendants of a failed colonization mission on Mars that had been left for dead by the Federation government. The Federation covered up its existence for years, claiming that all the colonists had died from an unknown disease, but unbeknownst to the Earth, a significant number of survivors had banded together to form a new nation on Mars known as the Vagan Empire. As the years passed, the Vagan Empire would battle the Earth Federation across the Earth Sphere, conspiring with corrupt Federation officials and deploying sleeper cells in preparation for a final offensive against the Earth itself.