Humanity spreads to the stars and forges a galactic civilization...
Fledgling nations arise from the ruins of the empire...
An ancient line of dragon-kings dies out as magic fades from the realm...
These are all examples of Microscope games.
In Microscope you build an epic history as you play, but you don't play the history from start to finish, marching along in chronological order. Instead, you build your history from the outside in. You start off knowing the big picture, the grand scheme of what happens, then you dive in and explore what happened in between, the how and why that shaped events.
You are free to jump backwards or forwards, zooming in or out to look at whatever you want, defying limits of time and space. Want to leap a thousand years into the future and see how an institution shaped society? Want to jump back to the childhood of the king you just saw assassinated and find out what made him such a hated ruler? That's normal in Microscope.
You have vast creative authority. You can make whole empires rise and fall at will. Dream up a utopia or destroy one with nuclear fire. You have that power, but remember you're not alone: every else at the table can do it too.
You create independently, but not in isolation. Each facet you add to history builds on what other players built before you. You expand on their ideas and the expand on yours. History might not turn out the way you expected. Be prepared to think on your feet.
When you zoom all the way in to a particular moment in time, all the players share the stage and role-play together to find out something we want to learn about the history. Did the crew of the Icarus know the aliens were in Titan? Did the rebels really fake the government crackdown? Do the knights remember the original meaning of their ritual vows? We role-play and see.
The more you play, the more your once simple summary becomes a detailed tapestry, full of meaning and surprises. History snowballs.