The rise and fall of the Eternal Empire and the Human Federation.
Background
Humanity had conquered the stars; an entire solar system within their grasp. To most species, they'd be unstoppable. However, humans, are, well... humans. Their homeworld never truly united, and different factions claimed new planets for themselves.
Eventually, in an effort to unite humanity, the Angel gave some humans a gift: magic. It is said that each of those humans tested in secret to see if they were worthy of wielding such power, though none know what that test was.
The Eternal Empire
One of those humans became known as the the Eternal Emperor. He, through some clever manipulation of both words and magic, united the warring factions of humanity under his rule, creating the Eternal Empire. He did not seem to pay much mind to the other human planets, or for anything beyond the human homeworld, for that matter.
The Eternal Empire lasted for a thousand years, all under the rule of this one man. He created a utopia of the Old World, without war. Science and technology developed in parallel with the newly discovered magic of the Angel, and for the first few centuries, the Empire did prosper.
Eventually, however, as all emperors do, the Eternal Emperor grew selfish and paranoid. He began to see threats everywhere, and the prosperity that he had created slowly declined. Interestingly, however, an outsider wouldn't have noticed this decline for a while; the Empire seemed to keep up appearances.
The Empire's fall was marked soon after. Groups of revolutionaries met in secret, plotting the downfall of their formerly all-powerful emperor. They were aided by defectors from the Eternal Emperor's own court, who were willing to sacrifice their lives for the cause.
The leader of this Revolution, a woman named Kiyo, killed the Emperor, but mysteriously disappeared only seconds later, as did the entire population of the Old World.
The Federation
While the Old World was under the control of the Eternal Emperor, other human planets discovered the existence of non-human life.
The Federation was quickly created to unite humanity out of fear of both the Emperor and the newly discovered aliens.
While the first few decades of the Federation's existence were rocky, the end of the cold war between human worlds allowed for much greater innovation now that secrecy was no longer a concern.
Once the Empire fell, the Federation issued a ban on travel to the Old World, as the disappearance of its entire population was suspicious (they still don't know what caused it).
Now
Approximately two hundred years following the Fall of the Eternal Empire.
The Federation is still in existence, though humans being human cause the occasional conflict.
The Old World is still officially off-limits, though some have managed to sneak in, and the Federation is aware of this. They want to know what caused the disappearance of its population, and to decipher its language and the strange magical artifacts it contained.
The Angel hasn't been seen since the Fall of the Eternal Empire.