Diplomatic Victory Resources?

I don't know that there are any resources specifically for the Diplomatic Victory. However, what you'll need to do is research the Alliances technology in the Civilization tree, and you'll need to be at least as strong as the nations that you want to ally with, because the AI Factions will only rarely ally with anyone weaker than they are. It will also help if you have positive diplomatic modifiers, such as the Diplomat sovereign profession, and give the factions you wish to ally with the occasional gift to help move relations towards friendly.

Other things that can help with improving relations are the mutually-beneficial treaties (like the Trade Treaty), common wars (but don't make a common enemy if it and your desired ally are both of the same alignment - the 'you attacked a fellow _' penalty tends to more than counter the 'we have common enemies' bonus). Nonaggression pacts can help keep the peace while you butter up someone to become an ally, but don't forget that you really should be the stronger partner in the alliance if you want the AI to accept the deal.

The last thing to remember about the Diplomatic Victory is that you don't need everyone allied to you to also be allied with one another (it'll help, because otherwise there's a decent chance that wars will flare up between your allies, which may force you to break at least one alliance, which will then really tick that former ally off), and you don't need to be allied to everyone. Once you have your desired set of allies, wipe everyone else out and you've won a "Diplomatic Victory". This is, in fact, the most likely way you'll win a diplomatic victory, because usually there's one or two hold-outs who just won't join the alliance for love or money despite being faced with a 10-1 power disparity if you factored in the strength of all your allies with yours and compared it to their strength (this is assuming that there are ~10 factions with roughly equal strength, or an equivalent situation where you and your allies make up ~90% of the total faction power in the game, which isn't that hard to imagine if you and your allies have been fighting and winning wars against non-allies).

As for why it's the red-headed stepchild - that's because it tends to be a pain in the butt to get the AI factions to accept an alliance treaty, even if you have a significant strength advantage over them, and because the Alliance Treaty is only available through a technology which you're only likely to research at a fairly late point in the game, which means that relations have had a lot of time to degrade due to close borders, the occasional war, competition over expansion space, refusals of stupid trades and Tribute Treaties, or whatever the other diplomatic modifiers come from. Then there's also the issue of not being able to back out of any of the treaties in the game until said treaty expires or an event pops up that allows you to either honor your agreement or break it. As a warning, random events such as Season of Blood (all factions are forced to declare war upon anyone with whom they are not allied) can make it very, very difficult to pull off a diplomatic victory after the event occurs.

Wow, thanks for the great and thorough reply! That really helps a lot.

One question... how does one actually start up an alliance? I have the alliance tech and good relations with a couple kingdoms. I already have a non aggression pacts and treaties with those kingdoms. The option to strike up an alliance is nowhere to be seen in the treaty window. Do they have to also have the tech or something? Is it a bug? Or am I just dense?

Thanks again!

You have to be stronger than the faction with which to want to make an alliance.  In my last campaign Tarth was stronger and would become an ally so I had to defeat them.  So if you want to achieve an alliance victory you should make an ally of anyone until you have defeated all the stronger factions.  You only need one faction to ally with you if all the others have been destroyed.

I do not think that the faction with which you are attempting to ally needs to have the Alliances technology in order for you to be able to ally with them, though I am not positive. However, your relations with that faction must be Close or better, while Non-Aggression Pacts must have relations not worse than Neutral and not better than Close; since you mention that you have Non-Aggression Pacts with some of your potential allies, you might not have good enough relations with them in order to form an alliance (and yes, I do think it's a bit odd that there is an upper limit to where on the relations scale you can form Non-Aggression Pacts, but I suppose it could be a reflection of the thought that the relations are so good that you don't need the piece of paper to trust the other guy not to stab you in the back, though since the pact also grants right of passage it's a bit odd).

It will also help if you're the stronger party, but that's more because faction power tends to have a positive effect on diplomatic relations in E:FE:LH than because faction power helps you intimidate others into joining your club or doing what you want them to, though I suppose the positive relations modifier from faction power could be seen as something representing intimidation.

They need to like you a lot before you can even offer.

As I understand it, relations always start as neutral, and you should be able to get treaties and caravans with factions you are neutral with. If you can get an economic or science treaty and caravans with a factions soon after you meet them that will give you +2 relations with them, which will help quite a lot in getting them to like you. Be prepared to pay gold for this, so clearly it helps if you have a certain amount of spare gold. Also be aware that relations get some big negative modifiers after season 100, so try to get treaties before then. Also declaring war on another faction which is on the same side (Kingdom / Empire, or good/ bad if you will), gets you a -3 modifier, so try to get good relations before declaring war on anyone. In general it will be slightly easier to get factions on the same side as you to good relations. The Oracle is quite literally mad, so don't expect her to be consistent in her opinion of you!

In practice the way I've got alliance victories in the past was where I got treaties with one of my neighbours, kept good relations with them until I was eventually able to get an alliance, and then eliminated the other factions. As you are allied with the only remaining faction, that's an alliance victory.

I think on one other occasion I had an alliance with one faction and ok relations with another, so I worked on improving my relations with the other until I could get an alliance with them too. If you are stronger than them and haven't declared war on one of their allies this isn't too hard. I think in the end I gave them lots of gold etc. to improve relations to Close, but this was quite a long time ago. At the point where you have an option to ally with them they will often pay you to do so, as you are generally stronger than them!

Beware of the Blood Season event, which puts all factions at war if they don't already have alliances.

So my main advice if you're aiming for an Alliance victory I guess would be to lay the foundations with treaties and caravans before season 100, and ideally before you've declared war on anyone. If you're struggling to get a faction to Close it's worth trying to bribe them.

My key to a diplomatic victory is to spend most of the game trying to build your relations with your desired allies, but then waiting until the very end of the game before actually creating your alliances (until all your desired allies are "close" with you).  Otherwise you might get pulled into unwanted wars if your Ally gets attacked.

In a recent game that I won as a custom kingdom, the blood season event hit and I ended up at war with everybody.  I then took a some cities from a couple of the empire factions, which elevated my place in the food chain a lot.  After a while, everybody made peace with me.  Eventually, I reached a point where there were 7 factions left (4 kingdoms and 3 empires), and all of the kingdoms were "close" with me..  Once this happened, I was able to create an alliance with all 4 kingdoms at the same time, and then I only have to destroy the 3 empires.  The more Allies you have, the less other factions you have to mop up at the end. However, the longer you wait to make ANY alliances at all, the more potential Allies you can get later.  Every time you create an Ally, you piss other factions off and risk getting dragged into their wars.  Therefore, wait until you can just make all your alliances in the same turn, so you don't have to worry about pissing off the factions that you want to make alliances with.

Minimum requirement is Yellow face for Non aggression pact, after that face changes to green from NAP.

Then you can ask him for alliance and it'll change from green to blue. Then wipe anyone else out. I had 3 allies the last time I tried it out. Timing is the key though, even empires and kingdoms joined my alliance despite the alliance maker being from a kingdom. Although I haven't dow'd anyone, everyone dow'd me. That helps.

If you're weaker than someone who's yellow to you.. they will want gildar or whatever until you reach the 0 and the number isn't showing red -123412something.  And after that, alliance lasts for only 99 turns, so don't lollygag around and focus on wiping out anyone that's not inside your alliance.

I think this is as simple as description on how to make it work can get.