Amor_Fati originally posted this question over on the forums, and I think it's a really interesting idea to debate. I also think Reddit might be a bit better platform for doing it, though. The forum thread is kind of jumbled. Below I've included Amor_Fati's original post as well as my response to the discussion that's gone down in the threat to start things off. I'm interested to hear what you all have to say!

Amor_Fati

Quite a bit offtopic here, but a nice theory that I would like to share. I've been reading the Sapiens book (and recommend it - it is a nice book), and a point the author (Yuval Noah Harari) makes is that humanity, through the course of history, moves itself towards unification. Since ancient times, we moved on (with ebbs and flows, gains and losses) towards unification.

When Cortez and his Spanish troops invaded the Aztec empire, the mesoamerican natives could not understand why they loved gold so much. In their eyes, it was a nice and shiny metal, which they could make good art, but it was inherently less valuable than other things like cocoa. Nowadays, there is nowhere - or almost nowhere - in the globe that cannot appreciate the value of money and gold.

While we have several nations, almost all the globe thinks and believes in roughly the same ideas - there should be law systems, democracy (even in autocracies there is some semblance of democracy), market economies, human rights, etc... Even as each nation and culture twists that ideas with some particular notions, they are still close enough to see the resemblance. Nowhere in the world today you would arrive with ocidental concepts like that and see the face that Montezuma did when Cortez waged wars to strip him off his gold.

And we see megaprojects today that transcend national borders - things like Antartic research (heck, most research done nowadays is made with multi-national teams), economic corporations, UN, and even space exploration - the International Space Station don't have its name for nothing. In other words, the "planetary unification" trope in sci0fi and in Stellaris does not means that there are not several nations in each world, but that if you zoom out and see that an space empire would be created by the effort of these nations helping each other, you can simply assume that the planet is a single entity (or a single goverment) and roll with it.