A Side is a faction involved in the conflict in Erfworld. It includes all units, cities, and terrain under the leadership of that Ruler.
The Ruler sets production for all the cities of his side. 
A Side does not need to have a city or capital. 
A Side ruled by a Royal can produce Noble and Royal units. 
A Royal Side can split off to become multiple Sides. 
A Royal Ruler may select a non-Royal as his Heir.