How can I help my resident cat adjust to a new cat in the household if it displays aggressive behavior towards the new arrival?

To help your resident cat adjust to a new cat displaying aggressive behavior, start by keeping them separated and gradually introduce them through scent swapping and supervised interactions. Provide separate resources like food, water, and litter boxes to prevent competition. Use positive reinforcement, such as treats and playtime, to encourage good behavior. Consult with a veterinarian or animal behaviorist for further guidance if needed.