The title's odd. What it was about was whether planets would have single governments.
I mentioned in the introduction that there are aesthetic reasons to have a single government to clear clutter out of the way, but the panel concentrated on the centripedal and centrifugal forces.
How was it settled? One colony? All immigrants are seeking out this colony to join it? That helps structure things.
Technology is important. When the American Civil War broke out, a good number of European observors thought it would break up a country that was, after all, impractically large.
Some questions about why so many worlds are depicted as medievaloid. I should have pointed out that the popular conception of the Middle Ages is that where civilization dropped. Indeed, from his comments, a fellow panelist believed that conception.
The ability to pack up and go elsewhere is important. Any unified movement that becomes a country hits fragmentation, if only in the form of children; a fellow panelist suggested contraception, except that would make the country extinct because you can't contracept the wrong-thinking out of existence.
Forms of government. I pointed to Greece and the riots as evidence that maybe democracy is not so secure in the saddle as many people would like to believe it. That too would have its impacts.