You can play Civilization 6 without ever founding a city—not even with your first Settler in the Ancient Era—but only kind of. I first tried this without modding Civ 6 at all, hoping that if I acted fast enough, I could level up my starting Warrior by finding settlements, and then successfully siege and take a city-state. This did not work.
As you can see in the screen above, Brussels easily defeated my Warrior, took my Settler, and I lost on turn 16. I hope that's a record. But I was determined to find a way to play Civ 6 without founding any cities, because once I decide on a stupid self-imposed rule there's no giving up. So I allowed myself only a slight change: I modified Eras.xml so that I would start in the Ancient Era with two Warriors and an Archer. I cheated, but only just enough to get off the ground. It's hardly even cheating, if you think about it, but please don't think about it.
Within minutes I had done it: I started a game, and without founding a city I captured a capital, Toronto. This is pretty impressive, considering I didn't cheat even a little bit. Not at all.
As a Canadian, I should probably be offended that Toronto is a city-state and not part of the great Canadian civilization. Really, I'm more bothered that they chose Toronto and not Quebec City or Montreal, both of which have greater history. But who cares: Canada is Aztec country now.
This whole scenario gives me an idea: what about a game where everyone starts with two Warriors and an Archer, but no Settler at all? The only way forward for each civ would be to capture a city-state as its capital. Sounds fun, though I'm doubtful the AI can handle it. I try it anyway.
On first attempt, it doesn't work at all. I forgot that when I conquered Toronto, I was playing as the Aztecs, who have a special Eagle Warrior unit that replaces the Ancient Era Warrior. With two regular Warriors and an Archer, there was no way I could capture a city state: my Archer could only do 15-21 damage per turn, and the city regenerated 20 health per turn. My Warriors, meanwhile, couldn't attack without losing most of their health and needing several turns to heal.
If you're wondering why that image is so orange, I was playing at 1 am (naturally, it's Civ) and forgot I had Flux on. You should use it. But also turn it off for screenshots. Anyway, I went back to mucking with Eras.xml to see if I could start with no Settler, two Warriors, and two Archers to make this work, but no matter what I did Civilization 6 seemed insistent on starting me with only one Archer. Eventually I got frustrated and just pasted a bunch of units in—and that's when it decided to work.
Well this is nice, isn't it? I have no problem taking a city-state as my capital with this army: in just nine turns, I capture Nan Madol. Unfortunately, the world rankings suggest my AI opponents aren't so clear on how to proceed. I lead in every victory category because they haven't captured cities. I give it a few more turns, but no luck. I'm the only one who knows how this game is played.
So let's go back to my first game, where everyone started with a Settler but I just chose not to use it. I may be dead broke (units cost upkeep money even if you don't have a city generating gold) but I've captured Toronto, and now I have my sights set on Buenos Aires.
Buenos Aries falls easily. I like that unprotected cities aren't a huge deal to take early on in Civ 6. But with all my troops scattered as I seek out new states to conquer, I become worried that I may be subject to the same treatment: my neighbor to the east, Egypt, randomly got in touch to tell me that my army is puny and I'm dumb. Or something like that. The point is that it was rude, and greatly displeased the people of Aztec-Canada.
Without declaring war, Cleopatra beings amassing troops near the border of Toronto. With my starting Settler still nestled in the city—which is sort of annoying because it means I can't hide Builders there during wartime—I begin moving troops to confront my Egyptian foes. It's time to see if, despite being behind by several turns of production and research, I can make an Ancient Era civilization mine.
Egypt only has two cities, Shedet and the capital, Râ-Kedet. I march toward the weaker city of Shedet, and thanks to my Archers and Aztec Eagle Warriors, I capture it without much trouble—even before my brand new catapult makes the trek from Toronto. Buenos Aires, meanwhile, is being defended from Civ 6's more aggressive Barbarians by a single Archer, which is a pain in the ass, but I manage to complete the Hanging Gardens there anyway. Things are looking pretty good for my no-city-founding playthrough.
I was always irked by how Civilization 5 discouraged conquering with revolts and unhappiness—not that bombarding a city with arrows and then marching in with axes wouldn't cause those things, but it was such a pain I typically installed puppet governments or razed cities when what I really wanted to do was expand my empire while keeping it under my creative control. To a degree, I think it was Civ 5's wording that turned me off—captured cities didn't really feel like mine, even if I got them up and running again.
I'm glad Civilization 6 simplifies this: Keeping a city no longer suspends its production, instead making it less productive until the war is over and it's negotiated for at the peace table. It's lost a bit of Civ 5's nuance—eg, installing a puppet government until the war is over, and then annexing only the best cities when you can afford to buy courthouses to cheer everyone up (when have they ever done that?)—but I feel much more encouraged to expand through war if that's what I want to do. And with my rule that I won't found any cities, it's the only way forward.
Instead of settling things at the peace table, though, I've decided to smash the peace table with an axe. Every few turns Cleopatra offers me a deal, even offering to let me keep Shedet, but I ignore her and march toward Râ-Kedet. Despite all her big talk, she didn't have much of an army at all (this was on Prince difficulty, so not too hard). Egypt falls to the Aztecs.
I never took an aggressive approach in Civ 5, preferring to expand on my own and turtle. But I was always annoyed by city-states hogging land I wanted, so much that I started turning them off altogether. Now that early wars aren't quite so much of a drain, though, I'm really enjoying being an all out warmonger in Civ 6. I would make a terrible world leader.
If you want to muck with the starting conditions yourself, it's pretty easy. Find your Civilization 6 install folder, which if it's in Steam's default location will be C:\Program Files (x86)\Steam\steamapps\common\Sid Meier's Civilization VI.
From there, navigate to \Base\Assets\Gameplay\Data and find Eras.xml. Make a copy of it to back it up, then open it in a text editor. Scroll down to the 'MajorStartingUnits' section and you'll find a bunch of lines which define which units players start with depending on the starting era, some with extra variables, such as 'AIOnly' which gives the AI extra units at harder difficulties.
If you want to start an Ancient Era game with an archer, for instance, you'd add the line:
<Row Era="ERA_ANCIENT" Unit="UNIT_ARCHER" NotStartTile="true"/>
I had to do some experimenting because as I mentioned, it mysteriously refused to accept my changes for a while (which probably just means I introduced a typo somewhere), but using the existing lines as examples you should be able to set up any starting units you like. Scroll further in the file and you can define starting buildings, governments, civics, and techs as well.
If I manage to win this game without ever founding a city, I'll let you know. But more likely, because it's what I always do with Civ, I'll get to the Renaissance Era and decide to start over with a new stupid rule.