Welcome to the forum!
First off, you are playing Huge/mara. I don't play those settings and those settings do present some unique factors. But what I do know is it does you no favors playing Huge/mara while learning the game, and you have a lot to learn here. In addition, for perspective, even on normal settings, your situation ..relatively speaking ...is far behind where you should be..but for mara that state would be even more pronounced. You are not in the "middle of the game" but very much in the late stages.
Settings aside, it appears you rolled a Fractal type map. Shuffle I believe is simply random mapmode that randomly chooses one of the various standard maps like fractal, pangaea, archipeligo, etc. You appear to have started in a semi-iso situation with Mansa Musa, who should be noted as one of the most unique characters in the game - more on that in a bit. Iso and semi-iso situations produce unique challenges in themselves that often require particular strategies.
One of the key factors of semi-iso generally is that you obviously only know one AI for quite some time. How you handle that AI may depend a good bit on who he/she is. But further on this key factor is that tech trading with that AI is almost a non-factor until other AIs are known. This slows things down for the human considerably. However, Mansa is unique in that he is the only one who trades with anybody regardless of the situation.
Point is, in a semi-iso situation, I might highly consider keeping the generally pacifist leader around for tech trading purposes and to have foreign trade routes available. This allows you to tech with more purpose and judiciously to set up tech trades, while, in this case, getting to Optics asap to go out a meet the world.
Anyway, that just an initial observation of your particular game. I would not call semi-iso necessarily rare, especially if you play Fractal maps often (which I actually do). But the above observations don't really help you learn the game from a basic standpoint.
As to your game itself, you are in a bit of a pickle. You appear to be playing without purpose here, which is not a criticism per se, and actually quite common for less experienced players. You are indeed very behind in tech. There may be some ways to remedy the situation, but in my honest opinion, I don't think that does you much good in terms of improving your gameplay...which leads to a very important concept I want to impress on you here:
The early game is the most important aspect of civ4. This is the area you really need to improve on right now. Once you do you can build off that progress.
Before I make my final recommendation to you, I will point out a few observations/flaws on the current state of your game:
1) Your civics are poor right now. Nationalism makes no sense right now if you are not actually using it for any purpose. In most cases, you will be in Bureaucracy as soon as you reach Civil Service and likely much of the game after, except maybe temporary switches to civics like Vassalage or Nationalism for army buildup in expectation of killing someone. Nationalism is mainly used for drafting
Mercantilism is really bad and denies you lucrative foreign trade routes, especially considering that all of your foreign trade routes are overseas and therefore more lucrative. Merc is something you might run temporarily in a Golden age for producing great people Same with Pacifism, which is a great civic if you have religion spread and run a golden age. Not terribly wrong to be in it, but you are not really using it either and it makes all those many units you have - for no purpose - more expensive.
2) Your economy on the other hand is not particularly bad. You make over 300 gold per turn (GPT) at 0% research. But you have so many useless units built. 36 Longbows! ..ha..there is no reason for that. Other than city MP..a unit in each city for happiness, you don't really need an army unless you plan to go to war '
3) Holy Shrine is not a reason for your failure here. In a majority of my games,regardless of whether I capture holy cities, or even founded my own at some point, I rarely have holy shrines. It's nice mind you, but it is not a major factor in success.
4) Not sure Great Wall was a good thing here. Mids is great and with stone no doubt I would go for that, but building GW in that city polluted that gene pool. Looks like you produced at least 3 Gspies which did you know favors here (unless you kept Mansa alive and used them for EP missions and stole a bunch of techs. That is a feasible approach on some levels but a much more advanced concept for you at this stage) Point that is you want to be producing Great Scientists early/mid-game and great merchants late game.
Anyway just a few observations there to take away but most of that is not what you need right now.
What I recommend is playing normal settings and maps. I would recommend normal speed/standard size with no huts/events and, for now, Pangaea maps. Pangaea maps I found more helpful for learning as you are presented with Diplo aspects earlier. It's just a given that your are going to meet most or all of the AIs very early in the game.
Play a shadow game here in this forum and get advice from the very start of the game ..turn 0. I assure you that just doing that a couple of time, even if only focusing on the first 100 turns or so of the game here, will totally change your perspective on how you play this game and lead to far more success for you. Basically a ground up approach.
, which allows us to build up our empire early on when happiness resources are limited.
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I was just hinting that right now they do nothing for you, therefore you could've settled some cities first.
