Hey there, it's me, Imperator_Knoedel from Reddit.
Taking a look at your most recent China save I notice a number of things:
First, Civics. Curiously, you never even researched Civil Service, even though it unlocks one of the most powerful civics there is. Also you built the Pyramids, unlocking all Government civics, but adopted Hereditary Rule, which is unlocked at a relatively early tech anyway. Usually when people construct the Pyramids it's to adopt the Representation civic, or maybe Police State if they want to warmonger, but for Hereditary Rule it's just a complete waste of production.
Second, Buildings. You build everything under the sun except Forges, one of the most important buildings there is. The production bonus it provides applies to everything your city produces, even if it's rushed via pop or gold or even if you are just plain building Wealth or Research.
Third, most importantly, number of cities. You have way way way too few cities, like an absurdly low number of them. Five wouldn't even be a decent number by 100BC, and now it's 1555AD. By now you should have literally every tile on your continent under control, but instead you haven't even explored it all yet. You seem to be stuck in the V way of thinking, assuming wide and tall are two ends of a spectrum and you can only be on one, but that's not true in IV. In IV expanding your empire can actually help your cities grow. For instance, in the southwestern corner of your continent are a Deer and a Crab resource, neither of which you have some of yet. The additional health they provide would help your currently unhealthy cities grow faster, or at all for that matter. There are so so sooooo many food resources and river tiles that are not being worked by any city, when you should have settled by them two thousand years ago.
Fourth, improvements. For the most part you seem to have done a somewhat decent job actually, but there's still some problems. It seems all your workers are currently asleep? You should have replaced the cottage on the Iron by Beijing with a mine long ago. In fact, most of the farms around Beijing should be villages or towns by now, boosted by Bureaucracy, but instead you employ a bunch of specialists. Guangzhou and especially Kyoto have lots of forests around them that should have been chopped ages ago. It's okay to keep like two or four forests around for health if they are on, like, dry plains or hills, but riverside forests should always be cut.
Fifth, diplomacy. You could have sold Replaceable Parts to Asoka for lots of cheaper backfill techs, and also sold him one of your many silk resources for 6 Gold per Turn. To be fair, it seems you were isolated for most of the game, so I won't blame you too much for this.
Overall the biggest issue I can see is that you have founded way too few cities. Now this game isn't yet completely lost, but what you really need to do is expand expand expand.
I took the liberty of playing a few turns to get you back on track to victory. I hope you appreciate the name I gave to the save.
Here's what I did:
I traded Replaceable Parts and World Map to Asoka in exchange for his World Map, 150 Gold, Priesthood, Civil Service, Aesthetics and Horseback Riding. I also sold him Silk for 6 Gold per Turn. Then I asked him nicely if he would be so kind as to gift me Divine Right, but he refused. Oh well.
I upgraded both your Triremes to Caravels and sent them to explore the world, hopefully to meet new civs and thus trade opportunities. New land to colonize would also be nice for the future, but as of now you have your hands full settling your home continent still. Incidentally I was the first to circumnavigate the world, huh. I met Frederick and his vassal, Wang Kon; I also met Suleiman and Justinian. With Frederick and Wang Kon I traded lots of techs.
I put all the workers to, well, work.
I researched Drama myself, everything else I traded.
I immediately (well I put one turn of production in first) whipped a settler in every single one of your cities.
I launched a Golden Age with the Great Engineer you had laying around and adopted the Universal Suffrage, Bureaucracy, Serfdom, and Mercantilism civics for the duration of it.
The move out of Hereditary Rule caused some unhappiness which I dealt with by raising the culture slider to 20%. I had Research at 0% and whatever I didn't put in Culture I had in Gold in order to rushbuy basic infrastructure (Granaries, Lighthouses, Forges, Courthouses) in the newly founded cities.
Two Great Prophets were born, I used one to build the Taoist Shrine in Kyoto, and put the other to sleep so that he might trigger a Golden Age sometime in the future.
Unfortunately a number of civs adopted Emancipation, causing even more unhappiness, and I ran out of techs to trade so I couldn't buy Democracy either.
On the last turn of the Golden Age I adopted the civics Representation, Slavery, Free Market and Organized Religion.
I trained some more settlers, you now have 17 cities, and should settle 3 more very soon.
Next turn you should whip the settlers in Kyoto and Guangzhou. Matter of fact, whenever one of your cities becomes even slightly unhealthy that's a good time to whip something. Musketmen or Longbowmen would be good candidates for now, many of the new cities I founded are without a garrison and there's two barbarian cities you should capture as soon as possible.
I marked several cities where you should or could build National Wonders. Oxford in Beijing and Wall Street in Kyoto are 100% the best locations, but I'm not that sure about where exactly to place Forbidden Palace and National Epic. Honestly, if you plan on adopting State Property down the line there isn't really a point to building the Forbidden Palace at all, but if you are sure you will stick with Free Market it might even make sense to build the Forbidden Palace on another continent you colonize, if you ever get around to it before the AI steals it from you. The National Epic should be placed in a city with good food so that it can run a number of specialists, and I marked several potential candidates.
Feel free to ask me any follow up questions.