The Dominion are a warlike group from Star Trek. They are based in the Gamma Quadrant.
The Dominion was founded thousands of years ago by shapeshifters who had been persecuted and killed by other races. In time, the shapeshifters built a vast empire by exerting their will on other species. Their military, the Jem'Hadar, were undefeated before they fought the Federation. In human history too persecution sometimes makes a person or a group warlike.
The Dominion is led by the Founders, shapeshifters who have become warlike from being persecuted. The second-most powerful race are the Vorta, who were "elevated" to sentient status after protecting a Founder. The Jem'Hadar are the warrior caste. They kill everything in their way and are addicted to a drug that only the Founders can provide to ensure loyalty.
Policy against the Dominion by Alpha Quadrant members demonstrated possible outcomes against a massive foe. The Federation tried to negotiate with them. This failed because the Founders refused peace. The Romulans and Cardassians launched a first strike. Their fleets were wiped out. The lesson here is that peace is usually the way to go, but sometimes it does not work so you need to prepare; a first strike against a foe you know little about is always a very, very, very BAD idea.