The Magical Kingdom was created some time after the destruction of Tilbury to keep those events from reoccuring. It is the goal and mission of the Magical Kingdom to completely control magic. As such, groups of Mages from the MK have traversed far and wide over Ara'niel, seeking to regulate such things. Those who do not submit are either killed or forced into submission. With the MK's high stature and incredible magical resources, it is no wonder that so many opt to kneel rather than stand against.
However, there are magical communities that do not adhere to the MK's regulation. For various reasons they refuse to submit, or simply do not agree with them. These communities are dubbed "Guilds". Guilds usually seek magical freedom in the face of destruction, persecution, or annexation from the MK. Members often hide when a group of Mages related to the MK pass through, relying on the populace not to alert them to his or her presence. For this reason, most guilds have a working function for a given region. They must effectively "buy out" the area they inhabit to preserve their independance. In exchange for the Guild's services, the local populace pays a blind eye when a visited by the MK.
There are some cases in which the MK is quite confident that a guild is in the area, and knows they won't recieve any information... without a 'gift'. The MK has been known to offer better services and politically endorse any area in exchange for guild whereabouts. In this way, they are taking over, one less guild at a time.
There are other cases in which the local populace is completely unaware of a guild's presence, either by concealing themselves so completely, or simply not having a base of operations. A wandering guild, especially those few in number, are much harder to locate and point out.
Then, there are guilds that are simply quite powerful. They offer exemplary services, or control artifacts that the MK simply can't compete with. The MK may or may not know of the existance of such guilds. In the case that it does, it either can't effectively muster the resources in the area to crush the powerful guild, or needn't bother. However, once easier matters are dealt with, all guilds will face the MK's might - for better or worse.
In the case where a magical group exists that is unaware of the MK, or where simple individuals are concerned, said instances are not referred to as guilds. If a group exists, such as that in Almeoth-Mardeo, that is and has been independant and contains much knowledge that the MK was previously unaware of or has yet to embrace, said instance is not referred to as a guild.