They are a various assortment of independent human planets. Some might be friendly with the TEC but want to maintain their independence, some might hate the TEC, but they are linked by the fact that they will defend their home territory vigorously, even if they have trade relations with the TEC.
Storywise, they're quite versatile and if you're writing a story they can be made to suit many purposes. On a grand scale, they're insignifigant and are getting crushed because of their failure to join the Trader Emergency Coalition, which would have protected them.
note: They might not neccesarily be human at all, but they use technology gained in trading with the TEC and they're not Advent or Vasari.