I don't really like the way trade has been implemented into the game, but it is a vital part of any victory that doesn't rely solely on fighting.
The AI seems not to have gotten the memo:

It was not for a lack of gold:

And would have helped those in need of stability:

I would like to point the role of the civic »isolationism«,

that most empire took at one point and might explain the result.

Yeah, I'm seeing Isolationism being picked more and more these days. I'm not sure if it's some unintentional side-effect from earlier AI tweaking (Also it's weird that in order to implement Isolationism, you need to first trade with everyone, but that's a discussion for another thread).

RedSirus wrote:

(Also it's weird that in order to implement Isolationism, you need to first trade with everyone, but that's a discussion for another thread).

Agreed! I'll let you create that one, I did my part lately...

I gotta ask though @cure_off how do you a pacifist run cause i cannot make it work for the life of me

Actually, that run wasn't that peaceful for a lot of turns, as I had to get vassalized and then to break free, which induced many stability issues (as you can see on the graph, it took me close to 250 to settle my cities).

I'm far from an expert, but I usually play peaceful games, as I find them very efficient against the AI.
MP is another beast. Most good players would simply crush me.

So, if I had to give some tips, for what they're worth, starting with the military: 

1. Focus on getting as many tribes as possible to get out of the neolithic with a enough manpower, the AI will not attack you if they feel you're strong enough
2. SKeep an army big enough for all the beginning of the game (until medieval). 
3. Early, I often place 2 archers, a spearman and warrior per town, and add then a third archer.
4. I tend to alternate between the troops and a district/infrastructure, not to crush completely my population growth, production (I rely often on workers at the beginning of the game) and influence
5. Although they do cost more, I tend to update troops in the medieval era, and sometimes after when getting powder. If the peaceful game goes well, you don't really need to bother to ever update your army after... And it's both great and somehow weird:

You can see, I started with many tribes (turn ~20), then saw an opportunity to get the achievement and dismissed my runners (turn ~75), got to no army and attacked as a result. While being vassalized, I built an army slowly and got my freedom (against the dark green player, probably around turn 120). As my opponent was way stronger, he fought 2 more wars. After that, we got to a standstill (turn ~150?). I completed my army a bit, and then did nothing at all on that front (the little upwards trend is probably due to adding towns and their garrisons, and placing a dude on each administrative center I had). The bump at the end is done by three IP towns (and the same garrison + AC thing). For a very longtime, I was also lagging behind on tech but it wasn't important (see below).

Other things to consider:

1. Trade! It is vital. The more they need your resources, the less they can attack you.
2. Offer to trade goods as soon as possible, even if there's nothing for you to trade, refusing trade is seen as an aggression
3. With most AI, having traded enough luxury gives access to strategic.
4. If you add another treaty, you can get them in an alliance most of the time.
   1. I tend to avoid the map and borders
   2. I obviously like to get the last one. If it's offered to you and are trading resources, you're pretty sure to get into an alliance if you ask for it
5. I'm not sure I've ever seen the AI break an alliance
6. When in an alliance, most of the time, you trade a lot, and war is not a question anymore
7. When your allied with many players, you can forget your army and anything going with it
8. I don't know if it has a massive impact, but I play often aesthete cultures (kinship)
9. I tend to avoid grievances, I renounce everything at the beginning of the game, except key territories, that I try to get. Most of the time, asking will only give them more WS.
10. Later, I usually ask for those that are »offered« through diplomacy, from players I don't fear anything.
    
    

I don't know if something in all that in anything but a tad obvious.
I'm pretty sure It can depend on the game settings too, I mostly play huge, 10 competitors maps, on endless speed.
Once again, I don't know if anything in it is worth more than the time, reading it, I'm an average player.

*Bump* because isolationism is really moving into overdrive these days.

One change that might be good to add to Isolationism is ways for other empires to "encourage" the isolated empire to drop it.  The Americans forced Meiji Japan to end its isolationism under threat of force, so it feels like we should still be able to request trade treaties with an isolationist empire, and maybe even form a grievance/demand for them to drop their isolationism under thread of war.

RedSirus wrote:

Yeah, I'm seeing Isolationism being picked more and more these days. I'm not sure if it's some unintentional side-effect from earlier AI tweaking (Also it's weird that in order to implement Isolationism, you need to first trade with everyone, but that's a discussion for another thread).

Yes,  I see the AI picking it a lot, even when it's clearly not in their favor.

It feels like every AI decision made by the devs is intended to encourage warmongering even more.

In this case, »Globalism« seems to be the choice better fitting a warmongering playstyle.
I found the game more enclined to push towards war during the first 3 eras. Then, I find it encourages peaceful plays. At least, from a solo experience.