Major
From BotF2-Wiki
Intro
A "Major", indeed a major race, is a playable race and represent an empire. There are Federation, Romulans, Klingons, Cardassians and Dominion.
Disable a major
There is an modding method to disable a major (source: http://botf2.star-trek-games.com/viewtopic.php?p=73872#p73872)
Edit Resources\Data\Civilizations.xml and change
<CivilizationType>Empire</CivilizationType>
to
<CivilizationType>MinorPower</CivilizationType>
or some of the other minor types (doesn't really matter, there's no difference).