A thieves' guild doesn't exist in a vacuum. It will be strongly influenced by the society which it is part of. Considering this is an important backdrop to the more specific matter of how a thieves' guild gets on with other associations and groups.
Size and Wealth of Communities[]
A first simple point is that a thieves' guild has to have enough work to support it! A small hamlet of 50 or so peasant farmers, most of whom are desperately poor, wouldn't support a single cutpurse, let alone a thieves' guild. A busy working town along a trade route, though, might well attract several thieves, even if the actual population was fairly low. If the village relied on monies passing through the place (coaching inns, hospitality, markets, etc.), it would be much richer in terms of money available for the thieves to filch than a place with the same population but dependent on the turnip harvest! In the design process, some specific rules for determining how many thieves various communities can support are given.
Social Alignment[]
The other factor which will always be of importance in determining the nature of a thieves' guild is the dominant social alignment (see the Dungeon Master's Guide, Chapter Four). Usually this will be reflected in the alignment of the rulers too, but this may not always be so: the possibility of a "divided alignment" society is discussed after the social alignments have been considered. Also, the following descriptions are tendencies, not absolutes. The final paragraphs on Special Social Factors shows how, for example, two Lawful Good societies dominated by different religions could have a very different view on thieves!
Lawful Good[]
Thievery will be strongly disapproved of—thieving is by definition unlawful, and few thieves are good. The penalties for thievery will be harsh, but will usually involve banishment, confiscation of goods, and long sentences of socially useful labor rather than death, mutilation (e.g., amputation of a hand) or such other cruel treatment. Lawful good rulers may go to some lengths to extirpate thieves' guilds, and lawful good people will certainly inform on thieves. There will be a strong sense of civic duty among such people to report any observations suggestive of thievery to the authorities. Tip for thieves: Find somewhere else.
Neutral Good[]
Thievery will not be disapproved of in the same way as in a lawful society, but thieves are rarely good, and neutral good societies are unlikely to have much regard for them. However, punishment for thievery may not be so severe, and the rulers may feel there are better things to do, and more important social priorities, than persecuting thieves. Assassins, for example, will be rated a much more important target for the authorities.
However, while the authorities (and society generally) may tolerate a certain level of thievery, there is likely to be a "threshold level" above which thieving will no longer be tolerated. Over-powerful thieves may be deemed a major social evil, and neutral good societies may be less fussy about the means (neutral) taken to achieve the ends (good). Do not forget that a viable interpretation of the neutral good philosophy is "war on evil without remittance or mercy," such that only direly evil ends will be eschewed in the prosecution of good! Certainly, plants, spies, moles within guilds—all may be used by the authorities against over-powerful thieves. Tip for thieves: Keep a low profile and you can get away with it, but otherwise—watch out!
Chaotic Good[]
Such societies do not often have effective, strong law enforcement, because the people prize personal freedom as a primary virtue. For this reason, thieves' guilds can grow strong in a Chaotic Good society. Even if the will is there to do something about the thieves, the means may not be adequate to the task.
The attitudes of ordinary people will be complex here. Some may regard thieves in a heroic light, as individualists and nonconformists, and be positively disposed to them. Others will regard thieves as taking the fruits of the labors of others away, and that this curtails personal freedoms—the undeservedly poor have not the freedom they should have. Reactions will tend to be individualistic (as with most Chaotic societies) and somewhat unpredictable. Tip for thieves: Stick around!
Lawful Neutral[]
This may be the most intolerant of all societies. Thievery is the very antithesis of law, and punishments for transgression are likely to be harsher and more cruel and unforgiving (e.g., amputation of a hand, a long sentence of forced labor) than in a Lawful Good society. Lawful Neutral rulers are likely to be rather stern, and worst of all, law enforcers are likely to be as numerous and unbribable here as anywhere. The only bonus for the thief is that Lawful Neutral societies are appallingly bureaucratic and its civil servants lacking in imagination and initiative.
Lawful Neutral citizens will snitch on a thief at the drop of a hat and, moreover, will do so out of a sense of real civic duty. Tip for the thief: Very dangerous, but definitely outsmartable. Faked papers and the like go a long way, and fast talking helps a great deal.
Neutral[]
Absolute Neutral rulers tend to be rare, except in countries which border on extreme alignment societies. Here, performing some kind of balancing act may be the only way to survive. Such rulers will probably ignore thievery unless it gets out of hand; they will have too much else to worry about. When it does get out of hand, their instinct will be to take whatever steps are necessary to restore the balance—more militia, more watch, more nightwatchmen and lamplighters in the streets, and so on. They will be highly pragmatic in their response.
While pure Neutral rulers may be rare, ordinary people will often be of this alignment. This reflects the fact that they aren't clearly of any other alignment: They're just pragmatic, doing what they need to get by day to day. Most medieval societies were hardly rich; even the "middle class" (until the 15th century in Europe) had a standard of living which could barely be termed comfortable. Survival is the name of the game, and clearly demarcated principles often go to the wall under such circumstances. The resulting blurred alignment can often be summarized as Neutral. Neutrals will tend to regard thievery as something they can't do a great deal about; thieves are mysterious, dangerous people with secret organizations. Neutrals look the other way; they don't want to get involved. Corruption can operate on a wide scale—it can even become a staple of commercial exchange. Tip for thieves: Good pickings!
Chaotic Neutral[]
Almost no societies, save for disorganized anarchies and some frontier lands, are dominated by this alignment. A Chaotic Neutral ruler is unlikely to survive for any time at all—ruled by whim and caprice, his subjects will likely rise up to put an end to such arbitrary rule.
Such societies, or ones comprised of Chaotic Neutral people, will likely not care a fig about thievery. Gambling, corruption, bawdery, muggings, and lowlife are likely to flourish in such societies, and thieves may grow very strong organizing such activities. Tip for thieves: Excellent pickings, and a strong guild can effectively rule such a society behind the scenes.
Lawful Evil[]
While, like all Lawful societies, Lawful Evil will not care for unlawful acts, Lawful Evil accepts what is necessary to maintain the strong in power. Fear rules here. If a Lawful Evil ruler uses thieves to backstab (literally!) his enemies, so be it. The ordinary people will cower if a thief swaggers around—providing that thief has the muscle to back any threats he makes. Thieves' guilds in such lands may be very strong, but they must have an emphasis on the brutal and thuggish to survive. Assassins will be stronger than thieves here, and the two may work closely together. Tip for thieves: Walk loudly and carry a big stick.
Neutral Evil[]
Neutral Evil is uncaring and unconcerned. Such people—rulers or ordinary folk—are out for what they can get. How one gets what one has in life doesn't matter at all. Neutral Evil folk are often cleverer than Lawful Evil ones, being more flexible and less respecting of a dumb "superior" just because he is in a position to push people around. They are also better organized by far than Chaotic Evil people. Neutral Evil is a flexible, smart, highly dangerous alignment.
Thieves have excellent chances here, but they will have to watch their own backs more than in any other society. Rival thieves' guilds may be particularly likely here. Since there is no stricture other than "don't get caught", competing guilds and gang wars are highly likely. Tip for thieves: Good prospects for the pragmatic amoralist.
Chaotic Evil[]
Such societies are likely always to be in ferment, since the arbitrary cruelty of the rulers will drive even a passive population to revolt before long. Only Chaotic Evil societies with a powerful clerical group, demonic presence, etc., will have the sheer force needed to tyrannize for any length of time.
At all levels of a Chaotic Evil society, backstabbing and intrigue, treachery and betrayal, is the basic coin of exchange. The strong take what they want however they like, and the rest are ground into the dirt. Since organization and cooperation are minimal, a thieves' guild where the members don't spend all their time backstabbing each other can grow to dominate behind the scenes very swiftly. Tip for thieves: Trust nobody, sell your granny into slavery, and have magic items allowing a fast exit.
Special Social Factors[]
There are many possible unusual social factors which will be an important backdrop to the role of thieves and their guilds in society. A few examples only are given here, since the possibilities are almost infinite.
Divided Alignments[]
Some societies exist where the alignment of the ruler(s) is sharply different from the general social alignment. For example, a lawful evil dictator might rule over a society mostly comprised of freedom-loving chaotics, enslaved by military might. Here, while the agents of law enforcement would have a very punitive attitude towards thieves, the common population might regard them as heroes, possibly giving shelter to a thief on the run, or at the least not giving the thief away.
Racial Divisions[]
Possibly the strongest antipathy between the races in many AD&D® campaigns is between elves and dwarves. This can strongly affect guild structures. In the worst case, a city might have an elven guild and a dwarven guild, both vying for humans to join their side, and with other races tending to ally one way or the other (gnomes might join dwarves, and halflings side with elves, for example). The antipathy of the two might override even alignment factors. This could break out into open warfare between the factions, or a long-running guerilla war could be the result.
Religious Factors[]
Not all societies with the same dominant alignment need have the same attitude toward thieves. One Lawful Good society might be dominated by priests of a god stressing mercy, forgiveness, and humility; another might be dominated by priests of a stern warrior god stressing protection, strength, and the need for justice to prevail in all circumstances. Their attitudes to thieves would be significantly different, to say the least!
Historical Factors[]
Thieves may be especially notorious (or maybe especially famous!) in a society for some unique historical reason. The people may speak of how brave Edrain the master thief backstabbed the wicked tyrant Baron Higsel and brought about the downfall of an evil tyranny. Hence thieves are somewhat better tolerated than elsewhere. Or they may speak of how evil Edrain the treacherous backstabber foully slew the greatly loved and wise Baron Higsel, the best ruler in the history of the land, and since this time thieves are deemed especially wicked, base, treacherous fellows and death is an automatic punishment for them! These are extremes, but the DM can easily envisage many variants on this kind of unique background.
All these general social backgrounds can easily merge into personal obsessions or idiosyncrasies of rulers, in dictatorial countries. There are many idiosyncratic reasons why a particular leader might have an especially punitive or lenient (less likely!) attitude to thieves than the general social alignment might suggest, but there should always be a good reason why. For example, a paladin ruler of a city-state might be unusually lenient toward thieves because a (Neutral Good) thief companion saved his life more than once in their adventuring days. Unlikely, admittedly, but possible! Such oddities should be thought up individually by the DM so that they fit with the campaign setting and history.