For the longest time, I've considered the game to be playable for 3-6 players. Initially, I really thought of it as a 4-6 player game, with 5-6 players being the game's sweet spot, but the difficulties of getting a big group together necessitated creating a 3 player setup. This is mostly related to getting the mix of which territories to include (and how many), and what mix of resource tiles (ie, capacities) to use, as you want the same level of tight-ness to persist across all player counts. The 3p setup I came up with was a good move, as there have been many playtests where only 3 of us were available.
And it seems to work pretty well. This past week, I decided to go further and try out a 2 player setup. Again, it's simply a matter of whittling some territories out, but it's harder the smaller you go, in particular because of the "# of territories" scoring category. Specifically, that category maxes out at 10 territories, but if the board only has 10 territories, then to max out that category, you have to wipe the other player off the board, which isn't very nice. But having too many territories could make things too loose, where the players don't need to interact too much. I tried it with 12 territories, but removed all of the capacity-5 territories, so all the territories are small, which encourages/forces you to expand a bit. I've solo-tested it 3 times so far, and it seems to work fine; in each case, players came into contact, had some battles, formed some trade routes, etc, so it seems promising.
Additionally, it is fast -- I can play it through in about 90 minutes. In contrast, 3p solo tests take me a full 3 hrs, typically. Why the discrepancy? I think it's just that I'm capable of playing at a pace of about 45 minutes per player but that third player (or the 4th, when I've done that) just divides the mind too much and each player's turn I'm forced to re-learn their strategy. There was an article on this subject recently, which basically says that the brain can juggle two tasks at a time, by setting each lobe working on a different task, but more than that is hard. I wonder if that's a consideration here.
Anyway, I've also made some dramatic changes to the structures system. I continue to be unhappy with the lack of place-specificity in the structures; ie, with most of them, if you want a colosseum, you're happy to build it anywhere, doesn't much matter which territory. And, I don't think the early-game structures actually help all that much.
So, I've added some new structures that give you token boosts (eg the Monument, that gives a Civil token every time you build in an adjacent territory), added language to many of the structures that applies their effects to adjacent territories, and added a couple of structures that require certain terrain (eg the Quarry that must be built in the mountains, eg). And I shuffled some of the existing structures around so they're available later in the game. I've tried this new framework in a 3p test and the 3 aforementioned 2p tests, and I really like the changes -- the early structures now feel like they let you lock in a strategy from a much earlier time in the game, and the extra tokens make it easier to implement Advances, which had historically been rather difficult.
The final change I've implemented is to add space "1" to the Unrest track, which up to now had started at 2. This also loosens things up. So overall, the game is a bit easier for the players, but still doesn't feel too easy, as I haven't seen scores that are downright explosive. The caveat is that I've never been an explosive scorer to begin with, so it will have to pass muster with some of the game's playtesters, most of whom are better players than me. But so far so good.