A Nation is a large body of people united by common descent, history, culture, or language, inhabiting a particular state or territory.
In Science Fiction, a Nation is usually depicted as the leading power of one planet, who unite with other Nations to form a League or Empire, etc.
A good example of a Nation would be a wealthy government located at the Heart or Capital of a planet.
A bad example would be a small committee of inferior life forms (in your universe) who live in a small apartment.
Usually, Nations will have their own military. This is often to keep order and peace in their lands, and to stop uprisings and revolts, but can also be used as a galactic fighting force to defend or attack.
They may also possess a fleet of warships to protect themselves from enemies or to assist in their allies’ struggles or fights.
Nations are often inferior to their League and do not create rules for their own planet. It is usually said that an Empire owns the land of the Nations included in the Empire. This would mean the Nation was inferior to the Empire and have to follow its rules.
Most Nations are named after their planets, but you can name them what you like, as long as there is some context surrounding the name. You wouldn’t call a Nation which occupies a dark, dreary waste planet The Nation of the Sun.
Nations overall don’t require a lot of planning or thinking, mainly because they are usually overshadowed by their intergalactic cousins. You really only need to focus on a select few. These will be situated on the planets your characters visit for a long period of time, or they will be significant to your plot.
This is a short post because I honestly ran out of things to say. The next post will be about Governments, which I think will be more enlightening.
I am also thinking about expanding the Planets post as I now see it is rather short for such an important aspect of Science Fiction.
Please let me know if you have any requests for Sci-Fi World Building, or if you want any other topics. I will be happy to include your suggestions as I feel it is important to involve the community.