The Dominators fought a long war with the United Planets in the 30th century. Several attempts to establish peace were attempted. In one of the earliest, the Legion of Super-Heroes escorted a Dominion diplomatic team to secret talks, and had to fend off attacks from people from Earth who were opposed to the talks.
Later, during the Earthwar, the war expanded involving the Khunds, the Dark Circle and even Mordru, but at the end of it, a peace treaty was finally achieved with the Dominion.
Though initially introduced as villains in the 30th century of the Legion of Super-Heroes, they appeared in the 20th century in the company-wide crossover Invasion!, in which they were the primary world behind the alien alliance that attacked Earth. Their primary motivation for this was their concern at the genetic potential of humanity, as evidenced by the large number of super-powered beings on the Earth. A Dominator created "gene-bomb" would affect many superheroes.
After Invasion!, a nameless Dominator played a significant role in the comic book one shot Blasters. This comic features heroes created by Dominator testing; they had wished to examine just how humans tended to gain super-powers. This testing involved running humans through a murderous obstacle course on the partly-correct theory that the stress would activate their "meta-genes" and cause superpowers. The "Blasters" are the ones who did gain powers.
Several Dominators were left on Earth for years and appeared in various comics (usually briefly). One Dominator would come under the control of the Queen Bee, presently the ruler of Bialya. Though this alien does not survive for long, its technology would cause trouble for the Justice League and the Global Guardians. Others appeared in Captain Atom (the Dominator became a farmer), in the Outsiders, in prison in Flash, and most recently in Superman.
A couple of Dominators, bounty hunters, pursue Green Lantern through the pages of his comic. Dominators played a major role in Keith Champagne's Green Lantern Corps.
In other media
The Dominators make a cameo appearance in Green Lantern: Emerald Knights as an alien race plaguing the early universe and the reason the Guardians create the first power rings. The story revolves around the first four lanterns fighting to defeat the Dominator fleet and discovering the ability to form constructs. While they are not stated to be Dominators on screen they are labeled as such in the commentary.
The CW 4 Part Crossover
The Dominators are the main antagonists during the CW event, Invasion. After Dominators land in Central City, Flash gathers his friends from across time and space to fend them off. It is revealed the they invaded in response to Flashpoint. The results of the incident caused the Dominators to see metahumans as too great a problem to ignore, so they decide to try to kill every metahuman on Earth before they became a threat.