Just thinking...
Space travel in fiction like Star Trek is just a hightech version of the Age of Exploration...
The same way that in the Age of Exploration Europe found never seen lands and cultures space travel in fiction find never seen planets and cultures.
Every planet has it's name based on it's civilization and these planets are a single nation-state in a similar way of the discovery of other civilizations in Age of Discovery. It's like if there were a Aztec planet, a India planet, a Ashanti planet...)