Two alicorns are looking over Dream Valley and reminiscing about their ancient world, the rise and fall of countries and empires and kingdoms, the changing environments, the fall of Equestria, and the extinction of alicorns.
NOTE: This can stand alone. However, for more information on Voodoo, check out "World of Quagga." Mardi Gras' story will be published at a later date, but she gives enough information to follow.
Now of you want to know what they are talking about more clearly, check out "Twilight Then; Twilight Now" by Tornado Firehooves [and several of his stories describe this timeline for more understanding].