The Antarans conquered all other races in the Galaxy and are using them as battle thralls for their next conquest, Earth (note: assume that it is like NuXCOM where every race is present on the battlefield):
Alkari: Floaters equivalent;
Bulrathi: Mutons equivalent;
Darlocks: Shapeshifters, posing as civilians or other aliens to fool you into sending too many or not enough soldiers against an unknown threat.
Elerians: Psi-combat ladies;
Gnolams: Cannon Fodder, their only saving grace is that their rolls have higher chances to succeed, and negatively effect X-COM rolls just by existing;
Klackons: Hive-mind buffs depending on the number of Klackons in sight;
Meklar: MEC troopers;
Mrrshan: Agile snipers;
Psilons: Sectoids with a different name;
Sakkras: Numerical superiority;
Silicoids: Naturally High Armor and Resistances;
Trialarians: Teleportation;
and the Antarans themselves are the masters of everything.
