10. Might Not Be Part Of The Federation
At the core of every Star Trek series is some form of the United Federation of Planets. Based out of Earth, the Federation is an affiliation of planets and species working together to make the galaxy a fair and habitable space. In addition to Earth, founding member worlds included Vulcan, Alpha Centauri, Andor and Tellar.
Oddly enough, Trill might not actually be a member world.
Many of the Trills encountered primarily on Deep Space Nine are members of Starfleet or work for the Federation. But at no point is it every explicitly stated that Trill is a Federation member world. Star Trek usually makes a point of making sure that kind of detail is clear, so not saying it is a member likely means it isn't.
The fact that so many Trills serve in Starfleet or work for the Federation does not mean that Trill itself is a member world, either. You don't have to be from a Federation member world to enlist in Starfleet, with Nog the Ferengi being a prime example of that.