Cats' fighting instincts stem from evolutionary and social factors. In the wild, fighting helps secure food, territory, and mates. As predators, their hunting behavior includes stalking and attacking. Socially, cats are territorial and establish hierarchies through confrontation. Male cats may fight for access to females.
Hormones like testosterone and emotions such as stress or fear can increase aggression. In domestic cats, this instinct varies by personality and upbringing, and responsible ownership involves understanding and managing these behaviors.