Instinctively, I find myself modeling a tribe of Dungeons & Dragons Orcs as similar to Klingons from Star Trek, or Vikings, or even a gang of bikers or skinheads.
But none of these models truly exemplify the vileness of chaotic evil, and in fact I have no idea how a band of chaotic evil beings like Orcs would behave "in reality".
Is there an historical example of a group or band/tribe of humans that match the definition of chaotic evil in Dungeons & Dragons?
The fundamental problem in finding a model for chaotic evil group to use as a model is the chaotic part. Any historical evil with a large scale hierarchy is going to be lawful evil or neutral evil. The great evils of the 20th century: Stalin's Soviet Union, Mao's China, Pol Pot's Cambodia, and Hitler's Germany are all very organized states with hierarchy. Pol Pot's is probably the least lawful and Hitler's Germany the most but I wouldn't call any chaotic. However, there is one item that was key to them (although less in the USSR and China) which might be useful: the inspiring leader. That provides a starting point to look for models.
Perhaps the best model I have for what I think real chaotic evil would look like is the movie The Warriors. Each band of orcs fights with the others and even among themselves unless a strong leader holds them in check. Such a leader has to be able to routinely deliver something: plunder, victims, food, in a much better way than happens without the submission to the leadership. Once that leadership breaks down some effort at revenge may occur but not much organized beyond that. Also, even while the leader is big others will threaten him, sometimes just for fun (which is a key point in the movie). This model of street gangs might be expanded to criminals in general although groups like La Costa Nostra again seem more lawful. Following up on the suggestion of criminals in prison I'd add the movie No Escape.
Another useful model, although again fictional and not historical, is in the old 90s supplement KViSR Rocks for the game Living Steel. Again, it follows the gang model. In it most individuals in an area have a disease which creates anti-social and violent outbursts. They are contained by gangs they are in and the gangs submit to regular combat with losing gaining better food. This fits the chaotic, individualist tendencies where the gangs are forced to choose between desire for victory versus wealth. It's a great book and if you can find it I think would be perfect for a "realistic" chaotic evil society.
Sorry I can't come up with something historical but I think those are some good models.
Unfortunately, people have built up a weird set of expectations around alignment over time that make this hard to do. "Well if someone's Chaotic then they never follow any rule and don't put their pants on half the days and and..."
I find the more effective way to treat the alignments is to realize that normal humans and humanoids are more lawful, chaotic, good, or evil than other groups, but not to a bizarre supernatural extreme.
Chaotic groups don't have to have zero rules. Lawful groups don't have to all be super-fascist. There is a "normal" level of having laws, sticking to both printed laws and social mores, and general adherence to the norm found in human societies, and that midpoint by definition is Neutral, and then there are those which are more individualist or more collectivist than the average.
From this interpretation, the American Indian tribes that Lewis and Clark came across (I just read Stephen Ambrose's Undaunted Courage) were largely Chaotic. The Americans came in and tried to set rules and broker peace between the tribes; all those agreements lasted till they were out of sight. Their stuff would get stolen anytime they turned their backs until they were so angry they were going to flip out. The Indians would lie and go back on their word in an instant. They lived in small nomadic groups. Now, they had religion and tribal rules and leaders (though practice varied, and the leader usually had to have proven himself the greatest warrior in some manner). That's a perfect Chaotic group example. As opposed to the American explorer group, which stuck to military rank, whipped members for breaking rules (the Indians thought that was bizarre and barbaric, and never beat their children because they thought it would make them less independent), considered laws and truces to be extremely binding... It was a classic Chaotic meets Lawful problem - not Firefly's Reavers meets the Nazis, but on those sides of the continuum nonetheless. Similarly, the early Americans themselves were more Chaotic (at both the personal liberty level and at the social/political decisionmaking level) than their British Empire forebears.
As for good versus evil - it's very interesting, they came across tribes that would help them without payment (Good), ones that would drive hard bargains and not help for free (Neutral), and then the tribes that even the other tribes described as "a-holes" that would rob and shoot you as soon as look at you unless sufficiently intimidated (Evil). I don't want to label any specific RL tribes, but that's the kind of real-world cultural variation you see that can fairly be described using the D&D alignment axis.
In contrast you have the native tribes of Central and South America, who were much more Lawful and created large empires - one of which, with all the heart-ripping, could be fairly described as Evil.
From a more modern day perspective, there are groups that are criminal or semi-criminal, and "have their own rules" but those are frankly more respected in the breach than the observance. Take the Sopranos depiction of the mob or the Sons of Anarchy depiction of a motorcycle gang - there's some lip service to "their code" but people violate it as much as they can get away with (and frequently more, hence the variety of shallow graves). Having some kind of basic rules does not make a group Lawful, it just makes it short of complete anarchy.
Some of this may be hard to conceive because there's a pretty good argument that if you're from America, Australia, or the UK, you do live in a Chaotic culture! We're #1, 2, and 3 on countries ranked by individualist vs collectivist tendencies. I suspect behavior in a truly collectivist Lawful culture would be more challenging for us to really depict because we're not steeped in it.
Real societies can't be "demon level" Chaotic Evil, because people have to eat, not get killed/arrested/etc by their enemies, etc., so some amount of banding together and having basic rules is needed. If you watch The Walking Dead, the band of guys Daryl falls in with that have their "couple simple rules" are a good example - they don't really stick by them except when it's convenient, but it provides just enough social cohesion that they don't just up and kill each other. That doesn't make them Lawful, it makes them "a Chaotic society."
In my mind, the best example of a Chaotic Evil human society could be a gang of bandits or a ship full of pirates. Evil, in that they don't care how they affect others in their pursuit of whatever goals they may have, and Chaotic in that they don't respect the laws of others, and their leadership is based on strength and ability to deliver plunder.
I'm not sure that this would really classify as a society, however, as such organizations are typically not self-sustaining, and draw new members from elsewhere, however this best fits the behavioral model suggested by "Chaotic Evil".
Another example could be any number of tribal cultures in their pre-civilization states - within their groups they are led by strong individuals and have social rules, but outside their tribes the rules break down, and captives from other tribes can be tortured and even eaten with relative impunity.
Humans are not really a good model for Chaotic Evil as in my mind humans tend more to being Lawful than truly Neutral, and chaotic evil human societies tend to be short-lived.
A Chaotic Evil species, however gregarious, would be composed of individuals who are impulsive and disorganized and who care more for their own goals than they do for other individuals' wellbeing. However, a gregarious species, however chaotic and evil, must have certain rules or else it could not successfully be gregarious. In such a species, within their social groups, "Evil" would be better described as "Caring more for one's own goals than for others' wellbeing" than "Needlessly cruel", and "Chaotic" could be defined as "Impulsive and disorganized".
That is not to say that a Chaotic Evil species such as Orcs are not "needlessly cruel" to those outside their social group - however disorganized they may be, they are sufficiently organized to be gregarious and must therefore have rudimental social contracts, however when they encounter individuals from outside their social group, they are not restrained by their social contract, and therefore those outsiders will be treated unfeelingly or cruelly in inverse proportion to their apparent strength; no matter how chaotic, a chaotic individual need not be idiotic.
To expand on this, a gang of chaotic evil orcs encountering a family of 0-level humans would likely treat them as delightfully noisy toys with a few trinkets to be squabbled over, then discard (or eat) their corpses after they died some hours or days later. On the other hand, the same gang of orcs encountering adventurers that the orcs know could wipe them out without breaking a sweat would most likely run and hide if at all possible, and if no opportunity for successful flight existed, would probably grovel and cower and swear allegiance to the adventurers if there was any possibility that they would be allowed to live, or else fight to the death on the off-chance that they might get lucky enough to escape if mercy was not an option.
It should therefore be relatively easy for a party of strong adventurers to find themselves with a band of orc lackeys, however they would also have to constantly guard themselves against their lackeys, since social contracts are typically weaker between different species, making the likelihood of the adventurers' erstwhile allies stabbing them in the back during a moment of weakness more likely. The likelihood of this would typically be proportional to the distance in alignment between the Chaotic Evil orcs and the adventurers - the more the adventurers direct the orcs to do what they like to do, the less likely the orcs are to feel stifled and want a way out - and also proportional to the current relative strengths of the adventurers and the orcs.
I'm not sure about whole societies becoming chaotic evil, but here are some societies that could be considered "chaotic." (Some contemporaries of these people may have had the audacity to call them "evil," but that's over-simplifying things.)
Some of these cultures had the "you rule what you can defeat" mentality to them. Pre-islamic Arabia operated on a "if my clan can defeat their clan, I can do whatever I want" mentality. That's supposedly the way chaotic evil societies work.
More accurate, I think, are the social structures of Gorillas. You have a dominant male, and subordinate males with more structure below them. The right to rule or lead comes from force, and chaotic-evil societies seem to consider personal fighting ability as "force."
Looking at the SRD description of Chaotic Evil, you see veins of chaotic-evilness in many different societies. Empires on the verge of collapse, for instance, could be considered chaotic evil.
Chaos is all about freedom. In terms of good, its freedom to live without the shackles and restrictions of rules that hold you back. In terms of evil, its freedom to do whatever the hell you like.
So chaotic evil creatures tend to only group together because it helps their selfish ways - in an Orc community, its less community and more loose association that provides safety and strength that the individual wouldn't otherwise have. That's the only reason the orcs gang together - and don't think for a second they care for the others in the group. its a dog-eat-dog world in CE, putting it politely. An orc would sell his grandmother if.. well if she hadn't sold him first, better stab her just to make sure.
As HerbN says, strong leadership is the only thing that gives a CE group some organisation - and that too, is for the benefit of the leader who'll consider all of his vassals as expendable. Expect a lot of contest for the leader position too, a lot of jockeying for position too. Popular conceptions of corporates spring to mind - with executives backstabbing each other for position, favour and whatever they can get away with.
You won't find many historical examples of CE, humans tend towards lawfulness as we form social groups only partly out of self-interest (its more an instinct for us, we're herd animals at heart :) ), and CE groups will be very small as they tend to disintegrate if a sub-group can break away, they will - some minor leader will want to be full leader of a group.
Alignment is a massive simplification of ethics and morality. But ethics and morality are massive, fluid, complicated things; there are literally infinite variations of conceivable philosophies on these subjects. To (ab)use a mathematics term, uncountably infinite variations.
So you cannot fit ethics and morality into one of nine little boxes, and expect anything like realism. You won’t get it. D&D’s alignment was designed, shockingly enough, for dungeon-delving and dragon-slaying, and not much more. The heroes are Good cuz they’re the heroes, the villains are Evil cuz they’re the villains, the dwarf is Lawful cuz he’s a dwarf, the orc is Chaotic cuz he’s an orc. You will run into problems literally the moment you step away from that level of simplicity. They start out small, but the more realistic you want to get, the more problematic alignment will be.
And law versus chaos is without a doubt the worse of the axes. While people have massively different ideas on what is good and what is evil, the concepts at least are reasonably clear. Law and chaos, though? I’d be shocked if you could find any two people who have exactly the same definitions of those two. I certain haven’t met any. The books are inconsistent, and oftentimes outright contradictory, on the definitions of them. There is a reason why no one ever published a Book of Unfettered Discord or Book of Perfect Dogma.
Thus, I don’t think you can hope for much more than a Hollywood depiction of barbaric savages, while turning a blind eye towards obvious questions of how such a culture could actually survive without killing itself, or just ditch alignment altogether and base the orcs on actual, real-life nomadic raider cultures. Which, yes, are going to have some strongly lawful elements, cuz it turns out the concept of “culture” requires some of those.
I think you should approach the question by looking at each aspect individually and try to find examples in the real world that make sense.
First, the idea of "Chaos" as a moral imperative can only really be defined by its social implications. If Lawful individuals are those who work within the constraints of a social contract where everyone gives up some freedoms so that they can benefit in some other way, a chaotic person would simply take what they want and do as they please. Would this make them unable to work together? No, it would just create a pecking order where everyone fell in line behind the strongest with each being bullied from above and bullying those below. The rule of might-makes-right would be paramount, but keep in mind that the "leader" of such a group would also understand that a lot of his might would be based upon a strong base of followers, as such, he would likely follow the normal gifting practices of "big man" societies, keeping what he desired for himself and allowing the rest to trickle down to his followers. In this way they would maintain control through a combination of fear and rewards. A good example of this would be the story of the Frankish king Morovous who would give out wealth to his followers, but when one questioned Morovous about the share he was given, Morovous split his head open with an ax.
Essentually, a lawful society creates rules that the individuals agree upon because they, to some extent, apply to all individuals in a fairly equal way. This provides a safety net for everyone, even those who give up some freedomes. A chaotic society would be inherently biased with no thought about "all men being equal".
As far as the "Evil" part. There is no such thing as good or evil. Such ideas are based upon perspective. Someone is only evil in comparison to someone that is believed to be good. An Orcs raiding and killing human for slaves and wealth is considered evil by the humans...but good by the Orcs.
While some of the comments suggest that Orcs would never care for one another (being chaotic evil) or compairing them to individuals with some type of anti-social behavious disorder, I would suggest that taking either of these approaches would not create a realistic culture or social order for the Orcs. Surly an Orc, being sentient will find some reason to care for his wife or children, even if it is only a feeling of pride of possession. Orcs will work together and form bonds to their mutual benefit and will see that it is reasonable to not betry the people you work with so that they will not betray you. To take these qualities away from any race just turns them into mindless insane animals incapable of any true interaction with members of their own kind...which clearly, in the case of Orcs, is not true.
People have deeply ingrained ideas about what alignment is, and it varies wildly from table to table (and from edition to edition). I've always liked the foreword explanation in the Alignment section of the 3.5e PHB - unlike nearly any other explanation, I felt it clearly identified and made very clear this basic rule;
Alignment is the means by which you go about your goals, not your goals themselves.
Except for certain characters (Paladins, Blackguards, and Outsiders) for whom their alignment is their purpose for existence, your alignment is meant to represent your outlook on the world, the rose-coloured glasses you wear rather than your actual eyeballs. A Chaotic Evil character has goals, and those goals might be the same as a Lawful Good character - it's how he goes about those goals that makes him Chaotic and Evil, not necessarily the goals themselves.
As such, a group of people with the same Alignment can be very, very different. But let's look at what makes Chaotic and Evil, well, Chaotic and Evil.
'Butterfly lemon pies!'
Chaotic characters or individuals are that tiny segment of the population that departs from Neutral (baseline) in the extent that they are able to adapt and roll with punches. When the plan goes off the rails, plows into a snowbank, and explodes, they thrive. Often they are seen by groups as 'stupid' or unintelligent, but if anything, the opposite is true - to thrive in chaos, you have to be able to analyze situations and come to workable solutions really really fast.
A good rule of thumb is that Chaotic characters are the kind of character who works and takes advantage of an existing situation, and a Lawful character is one who will try to change a situation to his or her preference. You can totally have a Lawful character whose modus operandi is to cause riots and wreak havoc - if that is his preferred environment, and he tries to create it whenever possible to achieve his goals.
If you think of a James Bond style character, a secret agent who goes into situations dressed in the right clothes, with a walther ppk, the right lie and split-second decisionmaking processes, that's a Chaotic character. Really, a 'fluid, evolving plan' is another way of saying 'Chaos'.
A chaotic character is an opportunist. They can have plans, but they drop them the first time they think of or see something better. They're always on the lookout for the next big thing, they play fast and loose, and often pick the short-term gain over the long one. Overall (on the larger stage of Nations and City-States), Chaotic tends to have short-term wins but ultimately be out-maneuvered by the long-range planning of Lawful.
Examples of Chaotic societies/groups; Mongols (Highly organized but very fluid in that organization and chain of command), later Roman empire (capable individuals promoted and given power, only way to maintain control of such a large area with poor communications), insurgency groups and intelligence agencies (rely on capable individuals taking advantage of opportunities).
Lawful societies/groups; modern corporations (corporate monoculture), modern bureaucracies (standardization over success), most of the Chinese Imperial periods (structure and form over capability), Banks throughout history.
'Kill them all, but make the children watch.'
Good and Evil are in some ways more straightforward than Chaotic and Lawful, but in other ways harder. People have very strong ideas and opinions about what Good and Evil are, but a lot of those ideas are societal or religious or philosophical and differ from person to person - much less what the hell an Umber Hulk thinks about utilitarian consequentialism vs catholic original sin.
Evil is about a complete lack of empathy.
When it comes down to it, empathy, caring about others by likening them to you, is the sole determining factor for the vast majority of humanity's morality - and it's the best starting point for defining Evil that you're probably going to find.
Now - people or monsters or devils or whatever might be sadistic, or might think that ripping people's toenails off is hilariously funny, or it's an important part of their culture, or whatever. I'm not going to talk about that. That might make them Detect as Evil, and it's probably much more common on the deeper end of the Alignment pool, but that comes under Goals, which is not what i'm discussing - i'm discussing Alignment.
When someone is Evil, they are going to go about their goals in an Evil manner. Which means, according to my view of it, they are going to get what they want in the absolute most callous way. Generally, even Neutral villains will try, perhaps not greatly, but at least a little, to mitigate suffering. When it costs them nothing, they'll let the prisoner have water. They'll not shoot the bystander during the Bank Robbery - they'll push them aside instead.
The Evil Character does not care. Why did they shoot that child? Because it was more amusing than not shooting the child. Why did they kill that hostage that was in the way? Marginally faster than pushing them out of the way. Wounded hostages slow police down more than unwounded ones - dead kidnappees can't tell the police details about their kidnapper. Someone cuts you off in traffic? Taping a pipe bomb to their exhaust pipe is a slight bit of satisfaction - worth ten times the effort.
Often without thinking about it, human beings (and other empathic creatures) try to limit or reduce the suffering of others they empathize with. Evil, simply doesn't. If someone can't do something for you, hurting or killing them gives you something you want, and no-one is going to get you for hurting or killing them, there's no compunction to stop the murder occurring - even if the reason is 'because I like murdering' or 'to get his candybar'.
Evil, as I view it, is simply psychopathy. There can be Evil characters who gain nothing or lose things by murder or violence, or any of the other traditional 'hallmarks of evil' and so just... don't do it. They can be lauded as the good and great in a society that isn't a weird faerunian 'society of murderers and bandits' (Zhentil Keep?), just because the rewards for not doing murder outweigh the reasons the character has to murder.
That said, when you have no empathy, there's little chance you're not screwing over others in some way. Competitive advantage is a real thing, and those with no compunctions about doing anything at all to gain it usually have bodies of some kind in the basement.
The Mongols were a semi-nomadic tribal structure based around the protection of a clan's warriors. If a slave of a clan was killed by a warrior of another clan, or a woman, or whatever, that clan sought redress, and if it wasn't met, there'd be a duel or an outright clan war.
That is a good example of an 'Evil' society, but it's scarcely the only one.
The Byzantines had an active class of nobles and a chaotic system of government based around backstabbing and betrayal. Empathy was an actively bad thing to have in the high tiers of their society, and turnover was high - ergo, the top tiers of their government were probably usually Evil (although crusading reformers play well with the mob and gain enough XP by going against the odds to take over periodically).
The problem though, is that there is no Human society that is Usually Evil. Most Humans are, by the alignment system, Neutral. Even giant jerks like the Assyrians are mostly passing fads. That said though, understanding an entire nation of psychopaths is not impossible, you just have to understand that on the whole, Empathy is good for nations.
So you can have Orcs that care about their families, or people they like (friends), but you can't have orcs that care about strangers or people they dislike. They'll screw those people over, and that's that - and in their society, that won't be weird.
But ultimately, what occurs in a society is largely a result of how that society keeps order, how it polices it's citizenry, how resources are kept safe from thieves, etc. Whether a Warlord rules with an iron fist (think of an african military dictatorship - crude rules enforced more with an eye to keeping people down than to fairness and justice), whether the orcs exist in Clans of individuals (by creed or by blood or by tradition) who band together for protection from other clans and enforce cooperation by means of brutal execution or torture or expulsion of clan members who break the rules without sufficient clout to get away with it, whether they have a highly stratified society where sometimes it's fine to murder people and other times if you do you get jailed and executed, all of these things will inform on orc society, or if it's a band of orcs, the society from which they come.
Notably, Orcs have negatives to the mental stats compared to humans - they will be less well organized, waste more time and effort with regular tasks, and get along less well amongst each other, so that will also inform their group actions.
But ultimately any society has to function to exist - it has to produce enough food to feed the populace, enough goods to trade, enough children to replace the deaths. The challenge is inventing a society which works with the Chaotic nature of Orcs, the Evil nature of Orcs, and the Stupid nature of Orcs, and still functions and exists - or at least seems enough like it might to fool your audience.
LotR and Warhammer solve this by making Orcs be born from the ground and eat anything. In DnD you don't normally have this option, so you need to actually sit down and think, about everything from ecology to foreign relations, to create a realistic set of Orcs for your world and setting.
A good example of a Chaotic character problem-solving.
Evil is about solving problems through other people's suffering, not suffering for it's own sake.
What about Chimpanzees? As a group they seem pretty chaotic to us humans. They are also one of the few species (besides humans) that are documented to have carried out tribal genocide.
Chaotic creatures don't organize themselves at big groups, at least not for long, that's their definition. So don't try to find behavior examples at governments or big societies. Chaotic groups like orc bands should behave like gangs, some criminal groups and weird collections of sociopaths. Their leader will be the stronger, meaner person, capable of keeping the others at bay, sometimes trough psycologic abuse just as much as physical. The others are scared of them or are just so dumb they don't trust their ability to lead. Some members of the group will be gathering courage to takeover and challenge the leader, and others will have tried it and failed and don't have courage to do it again.
The biggest mistake for me is trying to roleplay chaotic evil as a random killing machine. Every example of sociopath behavior in mankind has some sort of human side, even if sometimes distorted and corrupt. Each of the orcs will have similar behavior but different personalities, so some will be more violent, angry, impatient, while others will be smarter, more calm and negotiable. They will all engage in conflict with each other just like us humans engage in conflict with those we deal with all the time.
Imagine a band of teenage, drug-addicted, criminal, homeless orphans. That's the closer my imagination gets to someone born in a chaotic evil environment far from an organized society. They don't even know what's organization or lawfullness, they never seen it anywhere. They just dont plan in advance and do whatever feels right in short-term. They never plan in advance, they sometimes do something stupid and unnecessary, they have deep personal problems with those around him, even though they are the only ones they can count upon. And the one with stronger personality will take leadership and impose himself, but not easily or seamless.
The answers I have read so far seem to agree that chaotic evil analogs are difficult due to the possibility of evil being in charge of the governed body and therefore being lawful. If you accept this premise you need to look at smaller groups of outlaws that do evil for evils sake. At that point you are looking at the Charles Manson families and to a lesser extent organized crime families with gang initiations being a prime example of "evil for kicks". The knockout game would be an example of the chaotic evil inherent in some aspects of human society. But, as has been mentioned before, all of us possess both good and evil and will act in good or evil ways at different times. Alignment is far from static in reality.
Chaotics believe in the individual's right to decide and that combining into groups usually requires too many compromises to allow a creature to achieve the best in life (whatever that may be, guided by whether they are Good or Evil). So chaotic societies are generally going to be broken into small groups which share a lot of the same culture and goals, so there is little compromise needed.
Chaotic Evil societies are likely to be dominated by the strong, with the weak either cowed or tagging along to pick up the scraps left by the leaders. There is no conception of not "rocking the boat" for the good of all. If a leader is unable to dominate, s/he will be hung out to dry by the next strongest.
Only under extreme threats will large numbers band together for mutual support against some common enemy; the rest of the time other Chaotic Evil creatures will be the enemy as often as Lawful Good will be.
Chaotic Good societies may elect leaders for special needs - for example, forming a posse to hunt down some orcs, or picking a skilled diplomat to meet outsiders. Such leaders will have strictly temporary positions and will only be chosen if they can represent enough individuals' interests. Otherwise, those individuals are likely to request that they be picked. This can lead to squabbling, of course, but less so than with Evil creatures.
Alignment is not a reflection of reality, it is a representation of a fantasy reality where evil and good can actually physically affect the world - where being a bad person can result in your children being deformed or being a good person can result in straight teeth and hair that always looks nice even after falling in a swamp.
