The Three Systems
Fortunately for us, and perhaps unfortunately for the rest of the universe, the
Earth survived long enough for us to branch out to new worlds.  

This time, known as the
"Great Exodus," was a turning point in human history
for a number of reasons.  Though we had learned much during our time on
earth, there were still things beyond our grasp.  We learned to terraform
planets, making them more like the home we'd so callously destroyed.  We
learned how to create
d artificial gravity and how to protect the human body
during high-g maneuvers.  
Both of these things were essential to space travel.  

Try as
we might, we could not develop ships capable of traveling faster than
light.  We theorized how to create stable wormholes through space, a gate was
needed at each end for them to work.  So we did what we always do.  We sent
sent great colony ships, unimaginatively known as
"arks," out into the
universe.  Two of these managed to find suitable worlds for humans to inhabit.  
When we finally received their first messages, we learned two very important
things that would change th course of human history....

  1. We were alone in the universe
  2. They had completed constructing the wormhole gates

The humans remaining in the Sol system quickly went to work building their
own gates, and within a few generations, the interstellar gate network was
created.  By the time all three systems had been linked, terraforming was
already underway.  Humanity had reached for the stars, and now we would
bend them to our will.