So if you've ever played an RPG (tabletop or computer) you're probably familiar with the idea of jobs or classes.
Some of these can be easily explained away as they correspond (roughly anyway) to real world jobs or positions. A thief is someone who steals for a living, a knight is an aristocratic role with various responsibilities etc.
But a lot of the more exotic classes define an individual with a distinct (and often unique) set of combat abilities. Say sword techniques and battle magic known only to members of that class. Examples include things like DnD's Swordsage or Dragoons from Final Fantasy V.
I would like to include various groups in my world who resemble to a degree these classes and I'm looking for a way to explain their existence. Now presumably these individuals are part of some larger group, a kind of warrior guild. But what I'm wondering is does that actually make any sense? Particularly when you think that the various members of the group may not necessarily be aligned and could end up on different sides of a battle.
I'm primarily interested in combat based classes, non combat ones can be fairly easily described through guilds, religious orders and secret societies (which may also work for this question, but I'm not sure).
So my question is could an organisation exist with the following characteristics;
- Members are trained in various combat techniques known only to the organisation.
- Members can come from a variety of nations, species and backgrounds and will not always follow the same leaders. They can end up fighting each other on different sides of a battle or war.
- The organisation should be reasonably large. While individual masters training apprentices in the wild works for some classes, for others I would like them to be more numerous then this method would easily allow.
- The organisation may have some kind of fixed settlements or buildings where members are trained (though this is not essential)
If you can give real world examples of something similar as well that would be excellent, and I would also except an answer explaining why it is unlikely or not possible.
Edit: The marked duplicate doesn't answer my question as it pertains to more general aspects of RPGs / games being applied to the real world. I just want to take the idea of jobs and classes and give a sensible reason as to how and why they would exist. As far as I could see, none of the answers in the other question covered this.