I'd start with
this and see if there's an optimization:
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1950 AD finish.
Thanks to killercane and WastinTime for their saves, which I studied before playing. I should have read this thread too (didn't think of it at first), because I would have conducted my conquest path differently if I had realized that getting the latter AIs to vassalize was complicated.
My map:
No need for MapFinder on this game. I just regened a couple times looking for something decent. I wanted oil nearby to build KC's quick tank to capture the first AI, if possible. I also wanted forests and enough grassland for the workshops, and a food resource of course. As it turned out, I'd say my map was close to ideal, for these reasons:
1. I settled all three cities in the NW corner along a river travelling SE, toward all the AIs.
2. I had lots of space, while four of the AIs were cramped far to the east. This limited their expansion.
3. Roosy was very close. For some reason, he's extra slow to settle, maybe because he wants Seal escorts. Both KC and I wiped him out with one capture.
A few mistakes:
I was a little late on several tactics, but not too late. I figured out that OrgRel+UnivSuff was for cash rushing missionaries in 1t a couple turns after I got Hinduism, but before I started the GA. My first GP was a few turns later than optimum, because it didn't occur to me how important that was till about T8 (same time I started cash-rushing the misses). My other strategic mistake was to not attack Zara much sooner (he was isolated from all the other AIs to the south of me). This was a mistake because it's easier to get late AIs to vassalize if you kill off some AIs completely.
Strategy points to add to what all of you have discussed:
1. Key strategy for fastest conquest: Every city builds all units/buildings in ONE TURN if possible.
Comment: This is not just about workers in 1t to allow growth. This is about a game in which it's over in 30 turns!?! If you have 30t*3 cities, that's 90 units/buildings max (unless you run Nationhood). That's not much stuff to win with.
2. Set your finish goal. (Mine was way faster than the best to-date...
)
3. Minimize everything.
Comment: This is the Gnejs Principle. Think twice before you build anything or do anything. Do you have time to build it? Will it help you finish faster? Is there another way to get what you want faster, cheaper or better?
For example, do I want to build a settler? Isn't it better to rush the first AI, if I want another production city? That kills two birds with one stone.
Do I need the Pentagon? Well, I'm going to spam my religion for the ORgRel production bonus anyway, so I could just get those 2XP from Theocracy. With Vassalage, I have 7XP. Most of my battles started with my tanks fighting with about 60-80% odds, giving 3XP. That means they were at 10XP with each win. They never got to 17XP. My conclusion: No Pentagon.
4. Run Serfdom the entire game. (!?)
Comment: I realized that my workshops simply didn't need the CS hammer. Far more important to me was the ability to build those railroads and chop those forests in 1t. Now, I didn't start as fast as Indiansmoke proposes, so I don't know if that would make a difference, but I doubt it, because the missing hammers before the cities mature could come from a couple of chops. In general, my production cities had some outrageous amount of hammer overflow non-stop. (So this is another example of thinking minimally.)
5. Buy maps asap.
Comment: Critical for capturing the first AI and for planning the overall campaign.
6. Move the three marine together straight toward your first target.
Comment: You're guessing at first, but their primary mission is to capture the nearest city, or at least some workers. Think about it. Those semi-useless marines have no other use in this game, other than garrisoning your cities. These also means that your two explorers have two early missions, scouting the land for your 2nd and 3rd cities and meeting your neighbors asap so you can buy maps and move your marines there.
7. Capital builds workers, 1 per turn, until you have the 5th developed tile for your 5th citizen.
8. Connect coal and oil asap.
Comments: At Quick speed, Modern Age, you want to be able to start building railroads yesterday. If you also want to build the quick tank (KC's gambit), you need the oil. In any case, when that tank is built on around T6-T7, it should arrive at your target's front door, by rail, in 1t, with the 3 marines already waiting. You need lots of workers for all that work.
9. Only build workers in your capital.
Comment: Your secondary cities immediately go RAX-factory-plant-levee. They don't get the BUreau production bonus. THey don't have time for anything else, except the 2-3 missionaries you cash rush.
10. Avoid battle defeats, and kill off AIs completely or vassalize them with minimal damage.
Comments: There seem to be two main factors in vassalization: power and losses. If the AI is small, you want to kill him off completely, if possible. Leaving him in the game lowers the average power of all players, making other AIs feel more powerful and less likely to vassalize. If your target is big with lots of power, then you want to harm him minimally but still get him to capitulate. That means attack his 20%/plains cities and try to not have a single loss. A few early airships are better than artillery, because they don't die (=defeat), but you need to have a city within range to base them there. I built a couple artillery instead, but luckily decided not to use them against Stalin (I didn't know the mechanics at that point--I was lucky).
Those are my observations.
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I also thought about the idea of spamming some GAs for instant cities, but I didn't think of it till T8 and it was too late. I did capture a city or two, fully equipped with factories/plants/levees and lots of people. It would mean sacrificing the Theocracy 2XP. That hurts, because those CRIII tanks were significantly better than the CRII. All in all, my guess is that when you start pulling the victory date back into the 20s, you're not thinking about new production cities. You're thinking about getting your 3 tanks per turn started sooner and optimizing your vassalization path.
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While the general Hall of Fame is an ongoing competition, we are running a series of ten games called the Hall of Fame Challenge Series. Standard Hall of Fame rules (*) still apply, but your best submission meeting the settings of one of the games will be counted towards the Challenge.
, so the the game is almost done 
