Both the Dominators and the Dominated arose together. The Dominators were slightly more advanced when they reached the home continent of the other sapients, and so were able to defeat them and then make them a lower caste of their own society.
Through selective breeding and indoctrination, the Dominated were made completely loyal to their new masters, at some cost to their intelligence.
Together, they made enormous black cities and developed space flight. They conquered the entirety of their home universe and then moved into new ones.
The Daemons pushed the Notrox back to their homeworld and wiped them out. They razed and irradiated the planet's surface, leaving it dead, and then left to go back home.