The forces of Chaos include a multitude of lesser hosts which form the Chaos hordes, including bestial mutants, tribes of corrupted Ogryns, warbands of Renegade Knights.
Regardless, only those warlords most favoured by the Ruinous Powers can rise to to unite so many factions, as by nature the servants of Chaos remain in continuous war and competition with one another for the patronage and blessings of the Gods. Others may summon Daemons or call upon the Traitor Titan Legions. Others may incite hateful uprisings with cult demagogues or Dark Apostles. Influential warlords may barter with the Dark Magi of the Dark Mechanicum for possession of Daemon Engines. Chaos Space Marines rarely make war alone, with many of their operations involving other servants of the Ruinous Powers.