At the start of the game, each player starts in the safe (protected) zone, where you cannot be attacked by others. In this territory you are generally safe from danger and will have time to learn and develop your space station until you decide to leave the protected zone. Inside the zone is safe, but outside the zone there are much greater rewards and experiences to be had. After leaving, you cannot return to this zone.
Only players who later have their alliance HQs destroyed in war may be given a chance to re-enter the safe zone temporarily.
The safe zone in effect is just a territory owned by non-player alliances that help to protect it. Accordingly, this territory can be freed for capture by player alliances if they destroy the alliance buildings inside.