There's only one thing that's needed - a systematically voluntary society.
Since maintaining slavery is directly opposed to this, this very simple thing has become very complex.
If i had to guess, fixing and unifying the world peacefully is about, if not more complex than the colonization of the solar system.
That being said, the latter will be easier once the first is done.
It's actually quite simple.
That doesn't mean it might not be very complex in practice, although anchored on a basic idea.
Like BCH - decentralized digital cash.
