@silver-and-ivory:  Also: why should we have nations instead of familial tribes?

Nations are a lot bigger, more productive, and more flexible.

We want people to be able to roam around some without having to marry in to a tribe for protection, including being able to flee abusive family members.  This is feasible in a city-state, bigger nations such as France, or a collection of city-states.  Blood ties make this a lot harder.

While we also want them to share cultural elements such as language, they don’t need to share all cultural elements in order to have the necessary level of unity.  This makes it easier to satisfy peoples’ needs, which vary.

Nations are also much more productive, easier to physically defend.