According to cat behaviorists and veterinarians aggressive behavior in cats can have a variety of causes and even multiple causes. Stress is a major factor, which can be a medical issue and will need diagnosing and treating. A major cause of stress, however is environmental and can be easily remedied by we cat owners. (I use that term ‘owners’ quite loosely.)
If there is more than one cat in the household and they are not the best of friends, accommodations for their natural territoriality need to be implemented. For example they should not have to share food and water sources, or at least, not at the same time. Same for litter boxes. Each should have access to appealing places to hang out without having to traverse through another less-than-friendly cat’s territory. The little dog in the video below might not always be around to help out so whatever the cause of the one cat’s aggression, it will need remedying.
And whether or not there are multiple cats, all cats have basic needs beyond shelter, food and water. Cats need places to hideout and most cats like to have access to several secluded, comfortable spots. They also like to have access to elevated stations from which they can survey their territory and they need something to scratch on to pull off old claw sheaths.
A bored cat is a stressed cat so they need opportunity to play – especially important if they are indoor cats. Indoor/outdoor cats get a lot of stimulation, hunting, patrolling their territory and engaging with the world around them, including other cats. So indoor cats need toys and if you can manage it, play time with you.
Dr. Terri Koppe, owner and veterinarian at All About Cats first rules out a medical problem, then advises cat owners complaining of unwanted cat behavior by recommending the above implementations. It is often surprising simply changing the environment can solve litter box problems and aggressive behavior. If you want help in creating an environment which gives your cats what they need while creating an environment you enjoy, you might try Kate Benjamin and Jackson Galaxy’s book, Catification: Designing a Happy and Stylish Home for Your Cats and You.