Major

Intro

A "Major", indeed a major race, is a playable race and represent an empire. There are Federation, Romulans, Klingons, Cardassians and Dominion.

see http://supremacy.square7.ch/wiki-files/Data/Races.xlsx

Disable a major

There is an modding method to disable a major (source: http://botf2.star-trek-games.com/viewtopic.php?p=73872#p73872).

(In MP-mode it should be working be de-activating yellow button left of empire's name without the need of the following method)

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).