Proposed Canon
A Side is a group of characters and Units involved in the conflict in Erfworld and is led by a single Ruler, which is a King or Queen if the Unit is Royal, or an Overlord if not. The Side includes all Units, cities, and terrain under the leadership of that Ruler.
 Capital Sides
Capital sides (as the name implies) have capitals and are governed by a Ruler. A capital side can also own cities other than the capital. If the Ruler of a city is a Royal, the city may produce Noble and Royal Units. Royal sides sometimes split off into new sides.Erf-b1-p079a
 Starting a Capital Side
 Known capital sides:
- Ad Council LIAB Text 50
- Faq (destroyed by Gobwin Knob), now reestablished by Jillian under the protection of Transylvito
- Easteros (destroyed)
- el-Efbaum (destroyed)
- Gobwin Knob
- Goodminton (destroyed)
- Milquetoast (destroyed by Gobwin Knob)Erf-b1-p034
- Napster (destroyed)
- Paige Downs
- Sofa King
- Unaroyal (self destructed to prevent their units being killed and then decrypted by Gobwin Knob) summer-updates-043
- Westeregg (destroyed)
 Other sides
Non-capital sides (also referred to as natural allies) have no capital, no cities, no royals.Erf-b1-p079a They do, however, have their own treasuries and can form long semi-permanent alliances. If there is a way for Natural Allies to become a Capital Side, it has not been stated in the comic.
 Known natural allies Sides:
- Gobwins (used to be natural allies to Gobwin Knob)
- Hobgobwins (natural allies to Gobwin Knob)
- Marbits (seem to be former natural allies to Jetstone and/or Unaroyal)
It does not seem that Barbarians are a single side; rather, "Barbarian" is a catch all term used to describe Units without a side or neutral cities without a Ruler. If Rulers or their Heirs lose their capital they become Barbarians. All of the permanent inhabitants of the Magic Kingdom are Barbarian Casters.
From WB2014 Digdoug - Episode 8, it would seem that the total number of capital sides in Erfworld might be over 200. It wouldn't be surprising if the exact total number of possible sides in Erfworld was 255.