I played the challenger save
I settled 1W on the plains hill.
I smelled a rat (not entirely justified?) once I'd explored the map a little bit - I could see there was a powerful unit somewhere on the map because my warrior's health bar was really narrow. I think I was also expecting some 4-movement highly promoted bears or the like on the road so I didn't venture out until fairly late.
Therefore I built The Great Wall in 2280BC, before expanding to 3 cities and building the Pyramids in 1280BC.
Some philistines (hording barbarian spearmen) spawned in 675BC, and were so offended by the concept of No-Sex-On-The-Beach that they burned the city to the ground!
I expanded peacefully, leaving the Forbidden Fruits their quadrant and room for four cities.
Stalin declared war on Isabella in 825BC, and proceeded to march a whole bunch of units through my territory, eventually capturing one city (and leaving tons of units on my doorstep

) before making peace in 500AD.
At this point I decided it would be prudent to settle a gift city for Stalin, to get him to Pleased, reduce the chance that I'd be his next target, and give me the option of begging for 10 gold if he looks like trouble.
A few declarations of war later, Queen NO capitulated to the conspiracy theorists in 900AD, one turn after I dogpiled to try and pick up a couple of loosely defended cities.
These units now didn't have much to do, so I sent them to capture Flu, and persuade the Pathogens to give me their world map in exchange for peace - which demonstrated the need for Astronomy the the very least.
Stalin/Bolsanero kept his 35-unit stack right on my borders, so I felt threatened enough to do something about it - in 1140 AD I declared war with Elepults and Musketeers. He obligingly moved his stack onto flatland on my 100% cultural territory, so after sacrificing about 10 catapults, I was able to clean it up for relatively few losses and without a big war weariness hit.
My stack added trebuchets (1160) and eventually cuirassiers (lib->MT 1320).
I wiped out the forbidden fruit on the mainland by 1230, and she unvassaled herself and peaced out, so the rest of this was a question of invading mainland Conspiracia.
The early phases involved bombarding and then pummeling his stacks with my siege, capturing my liberated city in 1320, and his first proper city in 1370.
Once he'd mostly been drained of excess defenders, I was able to switch to two-mover style combat, and captured all his mainland cities by 1470.
I took peace for the low low price of Furs/Whales city The Giant Lasagna (probably my favourite of a good bunch of city names).

10 turns later I realised my units had nothing better to do than eliminate all the "We yearn to join our motherland" unhappiness, so they finished off both enemies in short order.
Mining Inc came in 1565, Statue of Liberty in 1580, and Assembly Line in 1585. From there it was a steady march to the finish... until the entire world declared war on the pathogens, and were entirely ineffective.

I finally joined in in 1800, capturing 5 cities on the first turn. I planned to take 4 more on the second turn, and one last one a turn later that wasn't accessible by coast.
However, he vassalled to Andrex Puppy immediately. It would have been awkward if it were the Nurses!
I waited until I launched my spaceship (one engine short, because I messed the timings up), before finishing off the war in 1832-34. Victory came in 1854.
Thanks for the game, DS. I got quite a laugh out of it.