Total War: Warhammer III diplomacy guide

The following guide to diplomacy has been penned by Doomykins of the Something Awful forums and donated to the wiki. It is meant to be primarily a guide for the Immortal Empires campaign mode, but the basic principles apply to any mode in Total War: Warhammer III. If you don't have the time to read it through, here are the key points:
# Identify 1-3 neighbors you can sign a non-aggression pact with so you can push safely in one direction and grow, 
# don't enter alliances without planning and avoid military alliances unless you have a very good idea of what you're getting into,
# never MA two powers that are next to each other, since that's a Catch-22 situation that ends with blood, 
# pay attention to the summary cards on the diplomacy screen.
Some of it might be applicable in real life as well!
==The Basics==
We've all been there. Your LL stack is pushing in Sigmar's chosen direction to take land that always belonged to you whether or not the residents knew it, your buildings are going up and will be ironclad in garrison defenses in 1 more turn, you have a bunch of cool friends and now with WH3 you can't wait to make a wacky gimmick theme army of Skaven Guns and Anybody Anything Else. Then some Beastmen run around raiding your land and threatening a rebellion in 3 turns, the guy 10 power rating above you declares, dashes in from fog of war, sieges your town and disables completion of the garrison, and two of your friends are going to war and you need to pick one and watch your reliability turn blood red because Khorne has just declared your heartland as the sight of his new favorite bloodbath.
Unless you are open palm slamming Karl Franz and playing This Is Total War with war declarations on every other faction you will want to know Diplomacy. 
===Why it matters===
Diplomacy is how I graduated to exclusively playing on Very Hard or Legendary Campaign difficulties. Diplomacy is how I push my armies to the limit, overstretch wildly and don't get punished for it. The #1 advantage to Diplomacy before huge fancy alliances and confederations is very simple: control how many people hate you and how many wars are going on. It's easier to attack, advance, expand and build up provinces in one direction then to do that while 3 other directions run at your heartland or decapitate any minors you aren't babysitting. The fastest way, guaranteed, to lose in the sandboxes of ME and IE are to be at war with too many people too soon and to be stabbed from all sides, bleeding out as you blubber "et tu, Tretch?" and he takes your laurel wreath.
=== Control your aggression ===
First thing's first: Control your aggression. Taking land because it is convenient, because it's next to you and you like complete provinces, is foolhardy. Your new borders have new neighbors. Your old neighbors hate you, so make a point to "clean your plate" and fully obliterate enemies or beat them until they accept peace so you can obliterate somebody else and then get back to finish them off. Keep in mind that the war gives them enough negative rep to never truly forgive you. If you're not lucky enough to be a corner or map border faction you have multiple directions jackasses can run in from and take your land.
How to implement it? Start the game, take a quick look at who is nearby and tolerates or likes you and try to get NAPs with them every turn. Be consistent. Don't jeopardize good neighbor borders because you want to take "just one minor settlement to complete the full province." Every faction you attack that has treaties with others and is feeding negative reputation to those factions.
:An ideal diplomatic start is to decide you're going to beat up your southwestern neighbor to convince your western neighbor that you're bros for life.
Now if anybody wants to attack you from the west they're more likely to be too busy wardeccing their neighbors and the guy on your west before they can even reach you. You don't need Alliances for this, the big bulky land between you and them is all the discouragement they need. Now you can take everything to the east in relative peace.
==Control Starts Early==
When you poof into a new campaign I want you to note who you start at war with, you're virtually always going to bowl them over and take their land for your starting province. Now hit that diplomacy button and look at who you are aware of and conversely who knows you exist. WH3 gives us Quick Deal and I want you to be checking that bad boy religiously every 1-2 turns until you've got your empire and a short history of its long-time friend set up.
Once you have your starter province look around you:
# Are there any natural barriers? 
# A big mountain range to your north so only Underway factions can approach? 
# Are there two people at war to your east, a LL and a minor? 
# Maybe there's a three settlement neutral minor to your west, and an ocean to your south?
At that point, hit Quick Deal and try to get Non Aggression Pact with that LL, or that big neutral. Make a friend. If you can get the treaty easily and the value is already positive then look over who they're fighting already, think ahead a bit, ask for some free money and snatch it up. If you're within .1 to .5 points of it consider giving them cash to get it. 
Once you get any treaty the rest are typically easier because the treaty itself gives positive reputation, NAP being the first step to the holy trinity: NAP, Trade, Military Access. These low-committal treaties are all you need to turn somebody into a campaign-long ally.
===Common mistakes===
A lot of new player mistakes happen here. You have 2 out of 3 settlements in a province and this triggers your military campaigner brain so you declare on that LL. You might defeat them narrowly, take all that nice land, get set up real pretty with neat borders but somebody who naturally hates you declares at the same time and attacks from an open side. The people that LL was fighting dec on you and occupy your attention since newly taken land needs time to get the garrison back up, at least. Your greed led you to get into 1-3+ avoidable fights so that you could click Issue Commandment once!
To avoid this:
# Look over your allies. 
# Look at their reasons for liking or hating you. 
# Pay very close attention to those other icons on the bottom right side of the screen telling you who they know and are dealing with. 
# Get those easy treaties. 
# Identify a safe direction to push in and use the veil of diplomacy to cover 1-3 of your other sides.
# Your goal here is to control your greed and keep a cool head.
==Make Big Friends But Hold No Feckless Alliances==
The holy trinity is so good because it can be dropped at any time with almost no penalties, particularly to reliability. They'll be mad you dropped treaties and you have to wait ten turns to declare to preserve your reliability but that's nothing compared to misplayed alliances. 
So you size up your neighbors, pick a winner or two, get those NAPs and fight somebody they don't like (i.e. aren't trading or allied with.) If they're at war with them even better, and if you can't get NAPs then "coincidentally" beating up the same guy is a fast shortcut to lifelong friendship. You can also as of WH3 take an ugly settlement in a bit of border gore and give it to somebody for free or even charge them for it, they'll read it as a wonderful +30-50 buddy points gift.
You have friends now! Between your new buffer state buddies and the natural defenses of the terrain, you're sitting pretty. One defensive stack on your border chokepoint and your LL can run wild. Now keep it under control going into mid game! Factions cannot declare on you if they've not met you short of a few very specific events. 
That's why you get to know people you have no choice but to meet and minimize your early expansion. 
That's why you don't send heroes and lords to explore without a very specific purpose. 
The more people you know the more RNG chances of trouble. If somebody declares on you from afar there are two bad possibilities. Nothing happens but they feed negative rep to anybody they have treaties with or they do that and send a crazy suicide squad halfway across the world to attack you. Having nice stable blocks of 2+ province buddies by your side fighting their own forever wars that keep things well clear of your breadbasket heartland provinces while you expand to a corner/map border is the dream.
===Why Alliances need to be carefully considered===
HOLD IT. I can see what you're about to do. "If we're all such good friends, we should use Alliance treaties." 
No! Never rush into an alliance without understanding the risks and NEVER stack multiple alliances, accepting as many as you can because "we're all friends here." 
There are two types, Defensive and Military. I will virtually never have a military alliance. I consider having more than one defensive alliance a big risk. I'll usually hold 1-3 defensives at most with my biggest, most stable neighbors who ideally aren't neighbors with each other. 
I've done this and still had them declare on each other later. When two alliance members who are also allied with you(or if you have two separate alliances with each) declare on each other you get a lose/lose choice: side with one, break with the other. There is no magic third button that tells them to get along or else. You might try to get a linked buddy blob going but it's never 100% safe.
The more alliances you have the greater the odds of idiocy and the only preventative cure is to keep careful track of who they're fighting. If Thorgrim is fighting Skaven, Greenskins, Vampires and a few of those are significant LL-led factions (Queek, Wurrzag, Vlad) then you've got really good odds of befriending Cathay who are fighting Ghorst, Vilitch, Snikch, etc. and it'll be a loooong time before they consider attacking one another. And even then they may still do it one day. 
The only mil alliances I've seen hold are the more natural ones (i.e. Empire/Dwarves Ordertide) or spontaneous ones like how I had two separate 4 faction alliances form of the various Chaos Demon/Warriors of Chaos armies in my Tretch campaign. If you must enter an alliance then at least commit and have members who are involved in a lot of fights as the AI weighs how many tough wars it is in before taking another on.
Military Alliances are even harsher because every time your friend declares war you're invited to do so too or get those awful, awful broken treaty anti-buddy points and Red Reliability, the kiss of diplomatic death and a 30-50 turn invitation to play on This Is Total War difficulty going forward. Ugh. 
What makes the holy trinity work so well is that other than getting and declining alliance offers between end turns you don't have to do anything to maintain them. If you're doing well and your strength rating rises and your reliability holds your friends will want to stay your friends in most cases. Even if they don't they'll let you know in advance by breaking treaties and even then they often won't declare for long periods of time.
==Reliability, Strength, Babysitting==
The most important thing for Diplomacy is to maintain your Reliability rating, which you'll do naturally if you follow the earlier advice and don't make Machiavellian land grabs. 
Your Reliability will almost always crater to that hateful red Very Low when you war dec early or break an alliance. Discontinue treaties from the diplomacy screen ahead of time (break, wait 10 turns) and mind who you ally with in the first place. When your Reliability is low you will be almost entirely unable to make any new treaties with anybody you don't have hundreds of positive reputation with and everybody will view you as a worthy target for war decs no matter how strong you are, which encourages others to help defeat you, which eventually leads to you being at war with 10-20+ factions as the rest steadily drop treaties with you. 
At least it'll be an exciting campaign if you're already winning and at strength 1!
Even if they are part of your victory conditions consider befriending powerful factions near you that you have mutual enemies with. You can set yourself up with a powerful economy, march some doomstacks over and blitzkrieg their core land to seal the win any time but you can't guarantee a secure start, especially on specific difficult LL starting positions. If you're going to nuke your Reliability then it better be for an even more important and well-considered reason than why you went into those Alliances in the first place. Or at least a really fun and thematic reason, like wanting to hold all of a continent because it's yours, damn it.
If you are doing well your strength rating should naturally rise. If you are not and it stays low or you have to make do with a single army for awhile then be wary. The AI is more likely to declare on you if they perceive you as weak. This is why rapid expansion can backfire, having a stronger built up economy and a garrison in every settlement can do a lot to keep enemy eyes focused on killing each other because you're too scary. Even then if you tank your reliability they'll find moral justification to challenge a powerful scoundrel like you.
Remember that while you're keeping tabs on who is allied with who, keep tabs on who fights who. You can get away with lower defenses and not expect a wardec from an enemy who while powerful is also currently fighting 3 other powerful factions. And now that you know that, maybe attacking one of them will make you a new friend, hmm? Strength Rating is a good number for gauging who you should care about, especially those powers rising to the top ten in your campaign. If you see a multi-power tide forming consider if you're too close to them for comfort or if you can join up, at least by getting the treaty trinity with as many of the individual members as possible.
My last little thought here is that as you get better at watching the affairs of your neighbors you may notice some of them getting blown out. If you have power to spare or your LL/doomstacks are in the area then consider blasting through your mutual enemy and gifting them back the land. An anemic buffer state won't last long and a small, weak buffer state won't protect you from enemy visibility near as much. If you neglect your friends for too long you'll soon have enemies at your borders and have to defend them yourself!
===Sic Transit Gloria Mundi===
Is that really it? Well, what makes Warhammer such a fantastic sandbox is how many hundreds of factions are at play with dozens being relevant and ideally no two campaigns ever playing exactly the same. You know the fundamentals so use them to make your early games safer because once your economy and elites are online you're much more free to do whatever you like. Diplomacy is a shield against failure spirals and early game dogpiles. As with all advice in this game once you're good enough you can get flexible and work around it.
Control your aggression and greed. Make a few powerful friends. Don't get roped into more commitment than you want. Be consistent and maintain your reliability. Pause frequently and study the state of regional powers and their relationships with each other. You can win by fighting who you want when you want but it sure is easier when somebody else does 50% of your border defense for you. And WH3 lets you build outposts and play with their units too! And here's a big secret: the AI cheats. But what if those cheats benefitted you? What if every minor faction neighbor and friend you had generated 1-3 stacks they can't afford and squatted in their capital all game, vastly discouraging enemy aggression? You could take that land, sure. Can you put 3 regular stacks on it to guard your border?
==Faction-specific notes==
*A few end-game crises change everything, such as Dawitide making all Dwarves hostile to everybody, or the Black Pyramid event making the usually passive Sentinels turn into the end-game bad guy faction. Mind that pyramid and those Karaks in your mountains. No, they won't care about prior relationships.
*Remember that several factions are canonical jackasses in the lore and will not get along with at least half the roster, typically Chaos/Evil vs Order/Prude: Skaven, Vampire Coast, Vampire Counts, Chaos of any variety, Greenskins and so on. This is represented by innate aversions. 
**There are also per faction rivalries such as Tomb Kings vs Bretonia, Dwarves vs Skaven, Tzeentch vs Nurgle, Slaanesh vs Khorne, Lizardmen vs Not Lizardmen, a lot of the VCoast LLs are set up to defeat each other for victory conditions, Aranesa hates Norsca, etc. 
**Some Lords have special passive penalties at start such as Imrik having big-dicked his way through Dwarf lands as the biggest prima donna and having a negative rep with his starting neighbors. If you want to be friends with factions that dislike you you need to find a punching bag or bribe them fast.
*There are also positive passive bonuses, though they are rarer. I've seen Tomb Kings start with +10-+15 rep because the Tomb Kings gave the Dwarves a good deal when the TK were alive and Dwarves never forget anything. If you see a positive bonus when you hover over the rep number and "why they like/hate us" pops up, capitalize on it. Although even with her passive +diplomacy bonuses Khalida has a high number of early aversions and undead malus declarations, stabilizing by mid-game once you start killing people nobody liked such as Skarbrand.
*The Empire cannot confederate Elector Count states normally, or all the other Empire sub-factions in the big valley bowl of humanity. The rule of thumb here is to keep your Imperial Authority at 3-4+ so you can confederate when prompted and absorb the -3 hit when prompted and to keep about 1000+ authority on hand at all times to put down ugly "Elector Counts decide a civil war is fun and games when Archeon comes to skullf*** them both at the same time" dilemmas.
*Ogres and Tomb Kings are technically True Neutral. Ogres can still start with aversions, though so far that has been to Skaven/Tretch. Zhao and Ogres have a high likelihood to get along and Greasus is positioned to get an enormous border buddy with him from the start. Tomb Kings make great neighbors because they are the only faction that likes great powers(or strategic threat as of WH3) more. If you start a game adjacent to Khotep, Settra or Khalida consider watching out for them a little and getting those treaties going, Tomb Kings AI scale absurdly well into easy Top 10 power slots and are loyal as all hell. Be careful of buddying up to Arkhan who is a Tomb King with the aversion flags of a bad guy faction as well as being anti-Tomb King to the other three LLs.
*Warriors of Chaos got enormous reworks and actual incentives to vassalize! Give it a try and consider deeply how much non-Dark Fortress land you want to hold and if you can give it to your little buddies instead for your precious buffer states. Make your enemies wade through dirty cheap rat bastard cheating AI stacks of Norscans to get to your breadbasket provinces. Otherwise remember: Chaos/Bad Guy aversions, people will get mad at you as you meet them unless you beat up their enemies and set up alliances.
*With a sultry exception! Slaanesh gets a load of modifiers to encourage them to befriend and seduce Humans, Elves and whatever else you've put on your f-list and doesn't autodec. Just remember how fast word gets around if you start setting up treaties with other bad guy factions: they hate those guys, you're befriending those guys, they hate you. You'll likely have to choose to seduce humanity or go Chaostide.
*Further Slaanesh exceptions include Morathi and Malus, who can use their specific gimmicks to start up something wonderful with demon factions they meet. Be wary of doing this with bad guy factions at war with other big Delf factions you want to buddy up to.
** While I'm here in Dark Elf town there is a real risk/reward situation where Hellebron and Morathi want to destroy each other for victory conditions. The benefit is great but this can do things like make Malekith fight you(or not) or deny you a wonderful AI ally. If you didn't actually want to conquer your starting continent then weigh the victory bonuses vs possible buddy state benefits, it may be easier or more fun to treaty them up and go raid Ulthuan. 
**Remember to always be scouting the situation before you make a hard declaration, I befriended Morathi as Hellebron in WH2 ME and it was the easiest Delf campaign of my life with my two enormous cheesy VH Delf deathball allies.
*Nakai must vassalize as he goes. You can shake them down for money every several turns at least and you really want your buffer state game to be on point to cover them from the side your Godzillas With Boxing Gloves Doomstack isn't painting.
*Bretonnia has the easiest diplomacy in the game. Keep an eye on your neighbors that look to be doing well, don't go to war with them, research and confed them automatically and get bonuses for confedding. So simple even inbred nobility can do it.
*Greenskins isn't as easy since you'll have to win fights but it is even more effective. Keep an eye on other Greenskin faction leaders, particularly LLs. Defeat them, take their stuff, get more powerful LLs for your forces. I once spent a ridiculous number of turns as Skarsnik using heroes to track Grimgor's stack in a ME round where he had 20+ provinces and 8+ armies. It took about 50 turns to not see him get auto-resolved somewhere before I could reach him but I eventually got the snipe and all that was his was now mine.
*Norsca has the same krump 'em and confed 'em mechanic but Norscan land is notoriously harder to defend. Things have definitely changed as of IE and The Big Map but be very wary of how much land you take as Norsca early and that you're making every other sea-faring faction nearby inevitably aware of you. In ME this often led to Delf and Helf declaring and storming your terrible, long travel time land that you couldn't afford an extra 1-2 stacks to defend early game. The primary appeal of the Norscan Aggressive Diplomacy Action is to beat down a Lord with a really good elite unit(mammoth, frost wyrm) and be careful to break the leadership of the prize in question but to stop focusing on it and let it retreat.
*Kemmler of the VCounts used to have an almost useless passive in WH2 to be friendly with Chaos that was removed by war decs as soon as Archaon spawned. In WH3 it is now possible to do anything with Chaos factions and you'll have loads of bad guy aversion points with many factions anyway so this is now a juicy bonus for getting big friends.
*Some factions get inflated Strength Rating passively and this will change how they act and others react to them. Most notably are the Tomb Kings who will eventually get multi-army access and transfer their free recruitment to always having many armies with elites active, and the Dark Elves who will eventually pile up loads of Black Arks.
*High Elves, Dwarves, Skaven and a few others have +Diplomacy bonuses hidden in their tech trees, rituals and hero/lord skill ups, such as Grey Seer Lords, Handmaiden of the Everqueen and so on. There isn't a limit to how many of these you can stack. Have ten high-level Grey Seers? +100 Diplomacy with Skaven. More practically you'll want to consider grabbing +diplomacy bonuses early if you can, such as with the Dwarf tech tree, because setting up friendships that become big later is easier if you can just crack that NAP.
*You can befriend some jackass wandering factions like Rogue Armies or Beastmen. Rogue Armies may even take settlements and become a power but for the most part these aren't great allies. They have a terrible tendency to meander around the land of people they're scared to declare on and raid them, they'll ignore your trespass warnings(but hey now you can dec for free any time) and they won't really follow orders or provide many ally benefits(the RArmies might but that's exceedingly rare to test.) In general, you want to declare and obliterate these guys to keep your lands clear so they don't dec and surprise you at a bad time later by finding your one worst-defended settlement. 
** There is a bug where Beastmen still generate money but have no use for it with all Beastmen units being free as of their WH2 rework so you can shoot for a NAP with Beastmen, ask them to balance it with gold and they might give you their starting 5k+, a real windfall if you get it.
*Some factions are not "true" factions and will ignore virtually 100% of diplomacy. The two big ones are the Sentinels of the Black Pyramid of Nagash and Clan Carrion of Nagashizzar. They will squat on their respective super spooky landmarks forever until you feel like fighting them or you get the Black Pyramid Endgame Crisis. Other AIs do go to war with them occasionally so you may be able to use enemy of my enemy to get positive points with them but they'll be neutral buffer states without it so not much incentive here. 
Category:Total War: Warhammer III