Generally, animals only fight if they feel they need to. It consumes energy and risks injury.
Animals fight, a lot. We don't see it so much with domestic animals because we define territory for them, and we provide food and mates (or sterilize them, mostly so they don't fight as much), and we select against interpersonal aggression (which is inherited behavior). Wild animals have to do all that for themselves, there's considerable selection FOR individuals who will fight, and they fight over those resources and sometimes just because they don't like someone. Chimpanzees and spotted hyenas have been observed waging deliberate war on neighboring populations, and the leading cause of death in hyenas is other hyenas. My well-fed free-range chickens would sometimes decide one of their number had to go, and that hen would be chased down and receive a sound thrashing for no visible reason (my roosters didn't fight, but my hens did, regularly). Most dogs LOVE a good fight; the only reason we don't see more fights is that we've bred it out of them. It's not at all unusual for animals to fight, within their own species or against a competing species, and sometimes the reason is evidently "I don't like your face."