There must be loads of smaller alliance wars going on, it is just as big to them as it would be to the bigger ones. The loses are % wise just the same so why can't we work out away where they can have their own Galactic Colosseum or if someone can come up with another option.
Deja Vu?
I do believe I recall a similar thread, albeit it did not propose a similar solution. It was at a time when the attitude of the forum was against the Coliseum (or was it before the Coliseum’s inception? <_<) being used for individual or small wars - anyway:
As it stands, I don't believe the lack of smaller-player/alliance participation is due to forum subsection, or as was the case back then, anti-small conflict sentiment - but to the fact that most new alliances simply don't bother/have never bothered posting.
This is due to the fact that most new players don't even register - or if they do, it is to use the market, spam temple, newbie section, or suggestion section

.
They do not normally think as part of a community, and so it doesn't really occur to them that when their three RL mates go at it against some cyberspace enemies - there is a whole community that might be interested in their exploits: They keep it to themselves.
I don't know if a subsection would change that detachment.
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Eh, all that said: with the new Phbb3, an additional subsection would not be messy - and it'd be worth a shot.