I've been exploring how achieve a conquest victory. The old classic strategy is simply raze everything as the Mongols by leveraging the fact that they don't lose stability for razing cities, but I wanted to get to a true, world-spanning empire, not a dozen cities surrounded by the rubble of the world's civilizations.
The basic theory is that because your stability doesn't change during a golden age, you must enter an extremely long golden age while stable to prevent collapse and preclude respawns. My first attempt was to try and roll a start (on Monarch/Marathon) where Silver Tree Fountain had already been built by Persia or Turkey in Central Asia. My plan was to grab the Great Mausoleum ASAP, avoid inventing patronage, and then launch 4-5 golden ages all at once, boosted by your UHV golden age and eventually the Taj Mahal. That would then give me enough time to complete WC. This didn't work, there just wasn't enough time to do it before coming out of the Golden Ages and dying, plus required a lot of luck in terms of what types of GPs are generated to ensure you have sufficient diversity.
My next attempt was with the Aztecs. The plan was basically to abuse the hell out of their Aztec Slave ability to be sacrificed in the capital to create a 3 turn golden age (on Marathon). The hurdles included:
1- Survive the conquerors
2- Catch up in tech
3- Capture whichever city had built the Emerald Buddha Temple (Kyoto in my game) and move palace there
4- Conquer everything while in golden age
And it worked! It was glorious. Surviving conquerors was easy enough. Step two was surprisingly easy. I'm not sure what causes it (either conversion to Catholicism or perhaps a pre-set game year?), but at some point tech costs absolutely dropped through the floor and I was able to catch up to Europeans incredibly quickly, to the point where I was the first to Representation despite only having the Aztec core cities, San Antonio, New Orleans, and Poplar Bluff as my empire.
Conquering Japan with a stack of cannons and musketeers was easy and I used 2 GPs to start a golden age while at Solid stability shortly before the invasion. That golden age would never end for the rest of the game. Kyoto quickly built a palace and I was able to begin sacrificing slaves to get keep a golden age going. Early East Asian conquests:
I followed with an invasion of Korea and China, slowly eating away at East Asia until both capitulated with only a few cities left. The sheer number of slaves I was creating was way more than I ever would have needed to keep a golden age going, so after moving my Palace back to Tenochtitlan, I began settling them in Kyoto. Each settled slave typically gives 2

and 1

, but with Emerald Buddha Temple, I could settle infinite slaves in Kyoto to create an absurd production city. I ended the game with 232 slaves settled and could complete any project or wonder in 1 turn.
From this point it was a slow steamroller across Eurasia from the East while then launching an invasion of Europe from the West (after conquering North America). My armies met near Constantinople. before splitting northwards to finish off Russia and southwards towards Africa and Indonesia.
My economy absolutely crashed around this time. The two things that saved me were the -75% number of cities maintenance modifier from Totalitarianism and the realization that, with Sagrada Familia and Central Planning modifiers, building wealth in Kyoto with 232 slaves and Isolationism granting +1

from specialists generated upwards of 7000 GPT. Eventually I realized it didn't even matter whether Kyoto was happy anymore; with 232 slaves the vast majority of the city's value was no longer tied to its population. In retrospect, the Temple really wasn't that important to the strategy, I could have made any city capital and just accepted that it would be perpetually unhappy. I finally went ahead and invented Radio. The combination of eternal golden age + GPT from Kyoto wealth let me run my economy at 90% science. Was almost done with unified theory at the time I conquered the last independent city.
It was a fun game. Some screenshots:
Late game Kyoto:
167 science Atomium:
238 science Global Seed Vault
157 GPT Westminster Palace
Wonders
Can you spot the moment I discovered I realized I could power my economy by building wealth in a city with 232 slaves while running Isolationism+Central Planning while having Sagrada Familia?