The Hawklands Millennium campaign has its roots in the Greyhawk fantasy setting from early Dungeons and Dragons lore. As a young DM (many decades ago) - I interpreted the "glosso-graphies" writing of the great sage Dr. Pluffet Smedger, which famously accompany "A Guide to the World of Greyhawk", as "current year one" - roughly 998 CY in game-time. This "error in start-date" interpretation later had huge creative benefits in providing a campaign-wide "historical gap" to enable my own plot machinations & "homebrew" designs. So the Hawklands was born, with the new City-state of Highfolk as the campaign players' central origins.
I've backfilled & "stretched out" the classic Greyhawk timeline events to work in my own model of the "Hawklands millennium" realm. God pantheons have been been merged & reorganized, major quasi-NPC's allegiances switched and even added another devastation event for good measure.