I considered am "Age" based game, where the world had various eras: the Age of Dragons, the Age of Conflict, the Age of Peace, the Age of Adventure, etc. But each Age wasn't applied retroactively to an era, but applied to a century at the start of that Age. At the heart of the world (or something) was the Throne of Ages, and whomever sat on it at the appropriate time could name the upcoming age, subtly changing the world, natural events, and the mindset of people.
The current age (Prosperity) would have been ending and entering an intra-Age period of chaos where elements of all the previous ages overlapped and people were unfocused. Meanwhile, various factions would be setting out to find the Throne of Ages and name the next age to be favourable to them and their faction.