At the beginning, there was only war: Gods constantly fighting for power over the universe.
After humanity took over, that battle continued.
Humans back then possesed extraordinary abilities that allowed them to do anything they wanted.
They used their power to fight for territory, wealth and influence.
After a very long time, a certain group had enough.
They created a barrier powerful enough to lock away humanity's powers forever, leaving them as weak as we are now.
Thanks to their efforts, we entered an age of relative peace.