Uh, there's a reason Rome is more recognized as the Roman Empire in textbooks. It had double the landmass of the Republic. It was way bigger.
EDIT: this Rome talk is pretty much derail at this point. Am dropping it.
That's mainly because the EK stagnated, especially when it's kings decided to hole themselves in Ba Sing Se and never come out.
Really, not what I was saying at all. I was saying that the Fire Nation is the same case as the EK, they're only united because there's a war to begin with. If FN was so consolidated with their propaganda, Zuko's transition to power wouldn't have been that smooth.
Plus it's not like it's that connected. We know that towns not near the FN's capitol really aren't that industrialized with The Search.
Rome is not a derail here. And yes, you're right, and it's my bad: I miswrote. I was trying to say that proportionally to the size of the original nation, the republic took significantly more land than the empire did, which is why their ability to keep everything under control was pretty decent.
I mean, we don't know how the EK formed, or when. You can say they stagnated, but we really don't know anything to judge that on. Like I said, medieval era france is a good analogue for what we see: a country where the king doesn't even have the power to enforce his will outside his own personal domain.
And I again don't agree with the FN being the same as the EK in that regard. There are vast geopraphical distances involved in the EK, there are vast cultural differences too, as we saw in "The Great Divide" between two groups that were literally next to each other, etc etc.
In the FN, we see a nation that's extremely well connected by good roads, railways, good shipping. This contributes a great deal to the erosion of regional cultures, due to the easier and greater internal migration, and of course the ability to move goods further and cheaper.
I also don't see what a few rural towns have to do with the unity of a nation, either. There's a difference between having rural towns and 75% of your country being a rural town and the other 25% is one stupidly large city.
On the propaganda; well, it convinced everyone for a century. Also, we have to remember that this is a country that's been fed "divine right to rule" - Azula's words there with that same propaganda for a long time, coupled with the previous Fire Lord being debended and defeated by the avatar who is actively propping up this new Fire Lord and some military defeats. Even then, I haven't read the comics but I know there's some conspiracy against Zuko in them.
Then again I don't read the comics because they're utter garbage and I hope they're not taken as canon by people.