Diplomacy is a very complicated thing. In some multiplayer games (not restricted to CV titles), diplomacy is undisputely the most important factor to victory. I don’t have any word to say for Dipoomacy in Multiplayer games, because people are smart, creative, and sometimes annoying spoiled kids. 
In single player games; however, the AI opponents can be viewed as dumb human players, who act according to predictable patterns. It is much easier to figure out some guidelines to crack AI’s brains. 
The purpose of this article is to discuss the diplomatic approaches used in a conquest-oriented game. This does not limit to a Conquest Victory, but generally applies to all games that the human player expands effectively and continuously.
If one expands extremely well, then there will be a Conquest Victory, or a Domination Victory. Otherwise one can still achieve Tech (space) Victory. Even if that is not possible, one can still aim for a Diplomatic Victory by adjusting the friend/foe ratio (mentioned later).
On this board there is an article “Triangle Diplomacy”, which is a very good read. This article of mine is a more generalized description of what we can do. In other words, you have to figure out a triangle, a hexagon, an axis, or an alliance yourself. Humans are creative.
I only have 3 general guidelines.
- Keep all your opponents equally weak.
- Keep as many foes as friends.
- Keep expanding!
Let me explain below.
1) Keep all your opponents equally weak
This is the core of diplomacy. Do you know why the English divides up the Muslim Middle East in the early 20th century? *cough*
Obviously, you will emerge as the winner if all your opponents are weak. The trouble is other people will do the same to you, by sponsering your life enemy under the table. Do you know how much weapons the US is going to “encourage” Taiwan to buy from them?
In CV4, you identify your stronger opponent at the time, and try to bribe the weaker ones to hate it (such as declaring a war). This involves some planning because you need to make friend with the weaker ones in advance. You must know that both bin Laden and Saddam Hussein used to be USA’s friends by now. Do you know why they were USA’s friends? Hint: they were both fighting against some other super power that no longer exist.
In practice, you look at the score list, and figure out who needs to be put down, and who will be put down if you don’t give them a lift. The high scorers sure needs to go down, and the bottom scorers not necessarily needs a lift (because of your limited power). Sure, it is fun to watch A put down B, but the consequence is A is going to merge B’s land and evolves into a monster. You want to be that monster, not somebody else. So your mission here is exactly to help B to defend against A, but not feeding B too much so B eats A alive. When I was little, the TV cartoon hero’s mission is always “help the weak to defend against the powerful”. They do this for a reason that’s not so naive, you see. 
Things are usually more complicated than just scores, because you will be able to pick sides. Do you want to join the Budda’s meditation class, or sing the chant of Hindu Blue? If you join one side, then you make CIvs on the other side hate you. Your powerful friend will become a headache, and your powerful enemy will also threaten your safety directly. This brings up the next guideline…
2) Keep as many foes as friends.
The most effective diplomacy in a war-oriented game is NOT about to make a lot of friends, but to make your friends and foes both busy at fighting each other, while staying on the winning side. Obviously, if you have too many enemies and too little friends, you enemies will overpower you and run you over. So it is easy to pick side at first — pick the side that will grant you SAFETY!
Less obviously, if you have too many friends, you friends will kill off all the enemies and prosper, or plot some conspiracy against you, and you have no way to stop your friends from surpassing you in score and tech. This isn’t the end of the world, though. You can always dump your friends. Saddam is on trial now, isn’t he?
It is actually a careful balance of friends and foes. If you see too many enemies, bring one down to restore the balance. If you have too many friends, bring one down to restore the balance. Notice the common phrase here — bring somebody down…! You are bringing down other Civs, one by one. Eventually you will be the only one left, hence the Conquest Victory comes.
The top scorers really needs to go fast. Friend or foe, you must bribe others to bring them down along with you. You are lucky if they are actually your neighbors, but what if they are not? Then you can either raze the cities, or give it to the underdog Civ who won’t develop into the next superpower to dethrone yourself. During the “bringing down the biggest threat, then the next, then the next” process, you balance the ratio of friend and foe, to keep them busy with each other. You match them up, A1 hates B1, A2 hates B2, A3 hates B3, or even better A1 also hates B2 and B3, etc. They will drag each other into war, and nobody is really gaining anything through all the war because they are all equally strong, or weak relative to you. Later on, you will have a much easier time to wipe them out.
It is also very beneficial to bribe your target to attack somebody else, about 10 turns before your grand backstab. 10 turns is about enough to get most of your target’s extra troops far away (or killed). Likewise, every time you go to war, make sure you can’t get backstabbed. If you can, make all nearby unfriendly Civs busy, so even if your target calls for help, nobody will come.
3) Keep Expanding!
This is really obvious, but easy to froget. I just include it for morale boosting reason. You know the drill. Keep expanding! You already have a good plan of the sequence of attack. On the first second you see the map clear, and the religions laid out, you form some plans of how you are going to win this game, right?
Here comes a real game example. Every game is different, but the techniques used are similar. One can never go wrong by being creative, too.
(click thumbnail to see full image)
In this link above, I have some simplified pictures of the map at different times. They are not totally to scale, just for reference. You may want to un-shrink the map on your web browser to see the fonts clearly.
In this game I am the Magenta Civ (Mao) on the very right end of the Standard Pangaea. Don’t worry about the city names – the leaders are matched to their color. To my left are:
Ghandi (purple)
Roosevelt (blue)
Saladin (dark green)
Isabella (pink)
Napolean (dark blue)
Bismark (dark grey)
Qin Shi Huang (yellow)
Montezuma (light green)
Elizebeth (light grey)
Mansa Musa (greenish brown)
Kublai Khan (brown)
Catherine (orange)
Alexander (blue-green)
1800 BC
My workers are hard choppers, and my axemen are swarming around like locusts. The international atomsphere is taking its shape. Ghandi founded Buddism earlier, and Bombay the Holy City is under my control. Lucky for me, Buddism spread to all of my religiously-fanatic neighbors, so they were all very happy with me (except Qin who declared war on me very soon.)
Apart from the Buddhism east, there is Hinduism west, slightly larger and centered on York (Elizebeth). Other Hindu members include Montezuma, Mansa Musa, Alexander, Catherine, and Kublai Khan. Around this time, Monty built a Oracle and founded Judaism, and later converted to it.
Liz’s New Hamshire was taken by Monty very early in the game, before I even met Liz and Monty. The outcome of this skirmish was that Liz was permenantly crippled, and Monty’s strong economical/military power was established.
Qin declared war on me while I was attacking Napolean, and by wiping Qin out later I made a big mistake. I gave Beijing (yellow BJ on the map) to Saladin, to avoid the death of an exposed, low health, but very highly experienced axeman. Saladin was the only Civ I’ve met at the time who was willing to take the gift, so I had no other choice. I should have just razed Beijing, and sacrifice that poor axeman. (more on the consequence later).
***
700BC.
With 9 cities to boot I was leading in score, followed closely by Saladin, then Monty. Saladin essentially took over all of Qin’s land thanks to my gift of Beijing. Saladin is quickly catching up in tech and he has cottage spawned a huge grassland around Mecca and Medina. My lead is disappearing. Although I am well protected by brother/sister Saladin, Isabella and Bismark, I don’t have any bright future.
My future is dim not only because my friend Saladin will outgrow me, but also the Hinduism west will unite and become a huge threat. Even Monty has a huge stack waiting. (see here Attachment 120672)
***
What can save me besides the map editor? You got it — Conquest-oriented Diplomacy! Dang Dang!
***
My great evil plan is to make a world war. I wish to keep the west busy and hate each other. They will keep fighting, weakening each other, while nobody gains anything, and I gain lands from the east.
Fortunately, since I own Buddhism, I can kill 2 birds with 1 baldy, well actually quite a few baldies. These bald missionaries will bring me incomes and friends. With my stream of baldies some Civs in the west will convert to Buddhism, become my friend, take my bribe to attack Hinduism Civs.
I can’t convert people without an Open Border, so I have to give them really cheap deals to get the +4 “Our trade relationship has been fair…” so the Hindu Civs’ will agree on an Open Border.
At this point I managed to Open Border with Mansa Musa, Catherine and Kublai. But I have to be careful not to convert everybody – I need as many foes as friends, so they will fight each other, and weaken themselves.
There is a simple pattern of AI’s conversion. If an AI doesn’t own a particular holy city, it will automatically convert to the religion that has the most popularity in its land. For example, Kubali Khan has 4 cities, 3 of them with Hinduism. He has a good reason to become a Hindu. However, after my missionaries added Budda’s shiny statue to ALL 4 of Kublai cities, he converted himself to Buddism. I don’t even have to ask and lose a tech. (Well, maybe Saladin or Isabella did )
If there are 2 or more equally popular religions, the AIs can be pursuaded to convert to any side. Another factor is the international atmosphere. Obviously one tries not to become the only pagen.
As you can see from my mini-map, Catherine is blocking Kublai’s way out, so they are a natural pair of archrival. I want Catherine and Kublai to go that way, even if they like each other now. So, I spread Buddhism to all of Kublai’s cities; he converts. However, I spared Cath’s Moscow and another city, so Cathy stays a Hindu, which is present in all of Catherine’s cities. I still spread Buddhism to other Catherine’s cities so I get some income from them from my Shrine.
Catherine and Kublai used to be close friends, but after Kublai’s flip, I easily bribed Cathy (the best backstabber according to Personality Matrix) to go after Kublai.
Another example I have is Mansa Musa and Alexander. Alexander helped Monty to attack Mansa before (Alex briefly converted to Judaism, but converted back to Hinduism later), so MM and Alex already dislike each other. Now since my baldies cannot enter Alexander’s land due to a lack of Open Border, I convert Mansa Musa to Buddhism. They are now even more likely to fight again in the future!
Just to make sure Mansa Musa the crazy tech racer is not doing the best he could, I bribed MM to go after Monty. He took one of Monty’s cities, and Monty took one of his. Excellent!
I also bribed Bismark to go after Monty, just to make them hate each other, and keep Monty’s attention away from me. (I am a paranoid, thinking Monty’s huge stack was intended to me). Monty’s stack of death sacked Bismark’s border city, but didn’t do so well on Hamburg’s tough defense. Monty didn’t use any catapult and simply threw them to the stone wall. Now Monty hates Bismark more than me, and I will be able to border Monty safer after I take Saladin’s northern territory.
Now the (miserable) future of the West is roughly decided; I can concentrate on the present east – my rival Saladin. The war isn’t the point of this article, so I will just tell you in brief. I bribing Saladin to go after Elizebeth, and mass produced all kinds of troops to backstab Saladin. If I didn’t bribe Saladin’s large maceman stack away, I don’t think I had a chance, though.
***
50 AD.
Finally I took over Saladin’s lands on the east. Interestingly, Saladin never pulled back his maceman, but to leave all of them in the west, defending London and other English cities, which he captured from Elizebeth (stupid AI. Any human player would give up those cities and rush back to defend homeland.)
My troop chased Saladin across the Pangaea, and finished him in a small town on the west coast. That town used to be a prosperous city of Mansa Musa, but Monty sacked it, and culturally it flipped to the English, only to be taken by Saladin a few turns later. Now this town is given away to Alexander by me, along with other former English cities. Alex has been in the bottom of the list for long enough.
Apparantly it is a weird decision of me to give 3 cities to Alex. York is the holy city of Hinduism. By giving it to Hindu Alex, I am pretty much gauranteed a Hindu Alex in the future, and sure he will not like me.
So why do I bother to make a potential enemy strong? Well, I really want to establish some enemies for Mansa Musa, the notorious tech racer. With a well-grwon Alex in the future, Mansa Musa will be surrounded by 3 hostiles, Monty, Alex and Catherine. (I bribed MM to attack Cathy later. You can see on the next map St. Peterburg was taken by MM’s musketeer, thanks to my free gunpowder.)
Just to summrize the relationships in the west.
Monty (Judaism) – Catherine (Hinduism) – Alexander (Hinduism)
vs.
Mansa Musa (Buddhism) – Bismark (Buddism) – Kublai Khan (Buddism)
Past wars:
MM –(attacked)–> Monty
Bismark –> Monty
Alexander –> MM
Catherine –> Kublai
Alexander –> Bismark
MM –> Catherine
Monty –> MM
***
380 AD.
With the west further “blanaced”, I had the free time to take out Isabella. Actually the war with Saladin cost me a few hundred years in tech development. I rushed to Chemistry by Liberalism. Before Liberalism I rushed Economics to get the free Great Merchant. Guess how much I got from MM’s capital? 6900G! I upgraded all of my assaulting melee units to Grenadiers, and still had more than 2000G left. Isabella, who has never seen war, became a victim of Grenadier + knight + musketeer + catapult sea rush. She went down on the 8th turn. If I had not bribed the western world to war on each other, they would definitely beat me on Economics and Liberalism at this point. (I beat MM of Economics by 2 turns.)
***
It is now clear that I am going to win. I will then take down the other Civs one by one, a friend, an enemy, a friend, an enemy, until there is nobody left. I think Bismark -> Monty -> MM -> Alex -> Cathy -> Kublai is a good route. 
To the power of Diplomacy!