From StarTrek.com: It is also a peaceful planet which has never been involved in a war. The technology is as advanced as Earth's; the architectural style of its cities is strictly functional rather than aesthetically pleasing. The society has no class levels. All beings on Edos are equal. Edos is not a member of the Federation. Rather, it remains in loose alliance with the Federation, coming under its agreements for trade, science, and aid in an emergency. 
Information from the Lincoln biography is not strictly canon, though the name of the planet seems to have been accepted in canon. See the full text of Arex's biography at Curt Danhauser's animated Star Trek site.