Thanks a lot for this post.
I tried a new save using the tips of the thread. As Carthage I managed to vassalize Arabia, Germany and Songhai. Egypt, Greece, Morroco and Ethiopia didn't vassalize and I kicked them out of the game. Songhai was veeeeery hard, it took almost 100 turns to finally beat them, and I had to beat 6 or 7 of their 15 cities.
But now the problem is with the Congress. England is trying the Global Liberation, and I don't have enough diplomacy to win, my only allies are my 3 vassals. I'm trying to restart 20 turns before, but there is nothing I can do to overcome this. Without my vassals I will have to face the Songhai all over again, and all my economy is broke without the vassals.
First of all, well done to the AI for being effective at using the world congress...Secondly, this game may have to be put down to a learning experience. As your new to Vox Populi it is reasonable to expect you with stumble to start with but you should take heart from the fact you have already made an improvement on your previous attempt. Even the best players get surpirsed sometimes, especially as the great people who keep it going and updated are constantly working the improve the AI so it is more challenging. Just the other day i was watching a youtube series where they restarted after around 10 hours playing as it seemed like the game was unwinnable.
Can you store enough gold to tide you over while you adjust your economy or reclaim your vassals? Sometimes it can seem like a dire position when things seem to be going so well and then you get hit by something huge like this but if you play it out it can often be salvaged.
How many cities do you currently own? As a warmonger who has defeated 7 other civs your empire should be quite large and you should have quite a large military so reclaiming vassals should not be as daunting as taking them in the first place aspecially as vassals tend to quickly fall behind in tech so your units should be more advanced.
Seemingly strange question for a domination game but do you need all the units you have? I often find that by mid to late domination game i have more units than i can even find things to do with having been provided large numbers of free units from policies, vassals and military city states and a lot can be disbanded which could save you a lot of gold and help tide you over. I usually put most of these free units on garrison duty in my cities for the passive benefits from garrisons but still end up with a load just sitting around doing nothing.
How are you looking in relation to the rest of the world? At this point you should be in a very strong position and looking at taking out the rest of the major civs with the hard part often being the time taken to mop up the rest of the map as you are in such a dominant position and i often find i end up finishing dominations game by other means as i have become so large i completely dominate all the others in other factors such as science, culture or by gobbling up all the city states as my allies and it is quicker to win the game by one of those means rather than do an official domination win.
One of the biggest weapons the AI can use against you that is difficult to counter is the world congress if you don't start working on it early (as you are finding out) and this is an example of how you still have to manage all aspects of the game and not just solely focus on your main win condition. By the time the world congress is founded you should be well established and as a warmonger have a large production base and lots of cities at your disposal so at least some should be dedicated to prodicing diplomats and great diplomats so that you can control a good number of city states and at least have a chance of influencing world congress votes and should at least have the option to propose them. When i am going warmonger in particular i start one city focusing on pumping out great diplomats as soon as possible so i can claim as many embasses as possible before the AI gets the opportunity (which they seem very good at these days) and once all embassess are claimed i use them to start leveraging city states from the AI. It is usually reasonably easy early game to control the city states in your immediate area by starting off doing quests for them and then topping them off with diplomats. If an AI is trying to steal my city state instead of just using the diplomat to bolster my influence i often camp a diplomat in their border and pop it only if i lose it as an ally to immediately flip it back.
What policie trees have you taken? There are a lot of thoughts on the policy path for domination games but i assume you have taken authority as the obvious choice but then you do have a lot of options available which can be used to bolster your strengths or protect your weaknesses.
If you get a good religion that can do a lot of the work for you so fealty can be a good choice to help you spread out your religion and dominate others to gain the maximum influence from it as well as being able to better expolit the bonuses available to your religion or other religions as when i conquer a city i try to make sure i have all that religions buildings and bonuses before i convert it. Fealty may not be needed so much for keeping your religion in a domination game as you can just counter other religions by taking their cities and converting them thus spreading your religion to others shouldn't really be hard and beliefs that give you bonuses to foriegn cities following your religion aren't much use as you should be conquering most foreign cities so you should focus on beliefs that benefit your cities. As you will have a lot of cities large faith generation should not be an issue either but fealty has a lot of nice general bonuses which work well with a wide empire or can help deal with some of the issues of a large empire and can help counter a religious focused AI you might have difficulty dealing with otherwise and the 25% reduction in faith costs are actually quite significant if you have a religion and looking to exploit it.
Statecraft will obviously help a lot with dealing with city states and give you greater influence in the world congress and it a popular option for me if i see another city state heavy civ in the game or i see a civ is focusing on city states and i don't think i can counter them easily by other means. Being able to purchace great diplomats after the industrial era can really help with controlling city states also and even if you don't have a religion you should be generating huge amounts of faith from all your cities and that is a great faith sink late game.
Progress can be useful as you will obviously end up with a lot of cities and you can get a lot of generally nice bonuses from having it although i find a lot of the bonuses from it aren't usually that useful for a domination game with the only thing that really draws me in a domination game is being able to purchase great writers after industrial era as spamming these can quickly push you through the policies and ideologies so you get early adopter ideology bonuses and get to important policies like iron fist to ensure you keep hold of your vassals as well as all that extra culture being excellent defense against high tourism civs.
Any of the industrial era policies can be good for domination but i am usually draw heavily to imperialism on anything but a pangea map. The bonuses to naval units alone are huge as well as the additional 2 air units per city which really speeds up late games conquering combined with the bonuses to so many tiles and then everything seems designed to benefit what your already doing...building military buildings, taking cities and fighting wars.
With imperialism and authority you will be getting huge amonts of science, culture and gold every time you take a city, your military will be extremely strong and an abundance of great generals and admirals can make life a lot easier. Agressive use of citadels can get you a strong foothold in enemy territory or can steal useful land and resources without having to take the city itself. Admirals can be used to heal all your ships so you can send them into situations where it would otherwise be suicide and they can be used to create more luxuries which can help combat spells of unhappiness from conquering cities so for me these two are the must have policy trees.
When it comes to ideology i am usually torn between order and autocracy. I usually pick order if i am deciding to settle down into going for another victory condition and using my vast empires resources to push for that victory type with order giving benefits to the type of empire i already have. If i am commiting to a pure domination victory i stick with autocracy as again it is so obviously designed to facilitate a domination victory. Iron fist obviously will secure your vassals and air supremacy providing free airports in every city is probably the stand out policy as being able to fly in reinforcements straight after taking a city is a massive game changer to conquering, especially when conquering over sea but also makes moving units around your large empire so much easier but virtually every policy in autocracy is designed to improve or benefit what you have already been doing as a warmonger.
Depending on how early i decide to settle into a none domination win i may take rationalism instead of imperialism as powering through the techs is needed for any victory and i won't be getting huge influxes of science from taking cities so much.