I started to trade around optics (and metal casting, to the very-behind Pacal) before meeting the continent with the AIs-who-have-too-much-land. That way, getting the cheap stuff like alphabet, monarchy, CoL, aesthetics, and feudalism wouldn't count towards WFYBTA for AIs who I haven't made contact with yet. I also got a cheap civil service from Gandhi, ruining my chem bulb (in my defense, I really wanted buro and especially irrigation).
After meeting everyone, I got a few more sweet trades in. Gandhi won lib, obviously, and I gave him astro for engineering + philosophy when I thought he was closing in so that he wouldn't lib astro and just ruin my trades. Instead of astro, then, the idiot got...divine right??? Peaceful AIs tend to do that, I don't know why...and he wasn't even the first to the tech, if I remembered correctly! Besides Gandhi, Mansa gave me nationalism for astro, and I got printing press for nationalism from Gandhi.
During the Renaissance, I was almost tech leader for a long while, but soon came to realize that there was a massive problem, likely intended by the creator of the map...a runaway India with 20+ cities. Gandhi pulled more and more ahead, blazing through the Renaissance era in short order and being first to the usual early industrial stuff that gives freebies (physics, communism). I decided I had to follow the philosophy of "take on the strongest AI in isolation, and the game is yours if you win that single war" - because the longer I ignored him, the more dangerous he got, and if he wasn't going to space, he was probably going to win culture by t250 or something crazy.
My idea was to get to steel and rifling and take him out before he got too dangerous by striking at his core, relying on the fact that he usually beelined culture techs like electricity or radio before ever touching rifling. However, my plan was disrupted when people got gunpowder and replaceable parts and started trading them around. Meanwhile, even without rifling her se, Gandhi was getting close to extremely dangerous stuff like assembly line and combustion. The distance was the real killer here...the cities best for whipping galleons were inconveniently placed, and necessitated launching an attack from the left of my empire, which meant ships took 7+ turns to reach his borders, even with circumnavigation bonus. By the time I got there, he had rifles and cavs, and I knew my collection of poorly-promoted cannons suddenly wouldn't be enough to take much, especially when soon up against machine guns and with reinforcements blocked by destroyers.
So...I reloaded, and instead of going communism like most games that drag on for this long, I devised a daring new strategy, something I've never done before - the artillery rush.
I bit the bullet and gave out steel for scientific method, and then steel + RP for physics. Hatty was getting rifling anyways (I learned that the hard way when I reloaded after a few AIs suddenly got it in a handful of turns), so I wouldn't have been able to hold on to that tech monopoly long regardless. Afterwards, I self-teched artillery, and meanwhile sailed off with a fleet of about 30 units, with a few stragglers that hopefully wouldn't die to destroyers. There was no time to wait for me to actually
get artillery on the invading fleet, as Gandhi was 3-turning the entire industrial era in rapid succession.
The plan was simple. I would take a few coastal cities with rifles + cannons (hopefully before he got rifles of his own, or worse, infantry), and then upgrade to artillery to push on. Taking out Gandhi's east coast will also hopefully reduce the amount of destroyers he can throw at me, and perhaps even kill some ships in port, increasing the likelihood that reinforcements can arrive safely. I realized that artillery specifically was the best solution I had to all the worries about this invasion. Facing machine guns or enemy cannons? They all count as siege units, so get destroyed even harder than rifles and cavs (artillery gets +50% vs siege; it's pretty neat). Worried about grenadier counterattacks? Cannons may die easily, but artilleries easily overpower a 12-strength unit, and can even stand up to cavs (and also can't be flanked by them). Because less artillery will die attacking, having a significantly higher base strength, I also solve the problem of all my cannons probably dying and me getting stranded in the middle of the war with no way to push on or reinforce, if I faced enough rifles and cavs. Worst-case scenario, even if he gets infantry or even tanks, artillery will have decent or even winning odds against them, especially when paired with airships. Meanwhile, because arties are a resourceless unit, they can be upgraded anywhere so long as it's your territory. I would upgrade my cannons as they go, and pray for the best.
Another pivotal choice I made was bringing my
woodsman III axe along for the ride, which acted as a superior medic (healing an extra 5% on the same time) - and when I attached a GG to him later, I got a free rifle with medic 1 as well, already bringing him up to par with a standard supermedic.
Despite trading for rifling midway into the war, I caught Gandhi at the critical moment when he didn't yet upgrade all his units. It also helped that I declared and bribed Mansa on him with MT + rifling a few turns before I actually landed, to maybe confuse him a bit and siphon away his stack onto attacking Mali. The coastal cities were garrisoned with medieval crap that I handily took care of, and I let him reinforce a bit before taking them. Miraculously enough,
his entire stack was pretty much just 12 units (I knew this by sending an explorer to constantly spy on his lands and keep tabs on his troops, that I deleted at the beginning of the war), and though he built some cavs to try to defend his capital, when I blasted them away with artillery and took the city, it broke him. He got infantry in the middle of the war, but two weren't enough to save Delhi, and afterwards, every city was filled with just one or two infantry, a machine gun or something else useless, and outdated pikes and crossbows he didn't upgrade. Funny enough, in the final city I took, I faced a tank (so he just got industrialism), which my CR2 artillery even got winning odds facing...none of this would've been possible with only cannons. I lost just 1-2 artillery the entire war, because airships softened up cities enough to where I got 60% win chance even against the toughest defenders. Against all odds, my artillery rush with what ended up being a pretty pathetically-sized army actually worked, because Gandhi did his Gandhi thing and refused to ever build units (or upgrade them, for that matter).
This is the final combined army size and conquered lands at the end of the war (I attacked both north and south of his empire at the same time, cutting apart the scant defenders, sometimes literally with a CRIII axe I wanted to upgrade but never got the change to). With about 40 units, that's certainly not a lot and would have completely died to any industrial-era AI besides Mr. "We never ever build units and work on Broadway while at war with 3 people".
After sweeping the guy from coast to coast, I capped him, and with 28 cities and at the top of the scoreboard, I am finally free to do as I see fit. I think I'll finish Mansa and/or Pacal, and then make this world pay with nuclear fire for what headache it has caused me (literally, a headache, from staying up to play too long). You thought this was a civ game? It's about to turn into Fallout 4

.