Sodom?
.....
Sparta kinda
I have made once a similar thread, but an ideology - to the minimum a gay-tolerating far-right, if not 'pink fachos'.
It's happened already, to an extent:
http://en.wikipedia.org/wiki/Etoro_tribe
(I know, it's Wikipedia, but it's the only online source I have on hand at the moment)
That just seems to be Pederasty, which s pointed out was quite common until the Christianization of the Western World.
Let's accept in this challenge a bisexual majority where homosexual relationships are preferred...
Sodom?
.....
Same problem, the country would soon go extinct. Particularly in the Ancient World women had to have babies early and often to stop the species from going extinct due to the high infant mortality rate.
Thus my use of the qualifier "to an extent".