Cats are very territorial as any cat owner knows. Introducing a new cat to the resident cat usually is usually a slow process, if you want the cats to get along and enjoy each other companionship.
Ideally, if you plan to have a multi-cat home, you should adopt the cats when are kittens. Litter mates will settle into a new home together and not have the territorial disputes that introducing a new cat into your home will create.
When you bring home a new cat, let the introduction to your resident cat be on the cat’s own terms. Bring the new cat home in a carrying crate and place the crate in a room and keep the room door closed for a few days. Place a litter box, food and water in the room with the new cat and spend time with your new cat in that room only.
This will give your new cat time to adjust to it’s new home and allow for the new cat and resident cat to sniff each other under the door. After a couple of days, open the door and allow the new cat and resident cat access to each other, supervise the meeting but don’t push. The cats will have to introduce themselves to each other on their own for it to be successful.
Expect hissing and growling and don’t try to intervene. The cats will have to work out their own territorial disputes.
Continue to maintain each cat in their separate locations for a week while they work out their disputes. Then slowly try to bring the cats together with a cat toy and play time, and begin to move their feeding and watering bowls closer together.
For most cat introductions, this will take some time and patience on your part, while each cat determines which part of the house is theirs.
If you already have a multi-cat household and have problems with your cats getting along, this method will work for a re-introduction for the cats. Separate and separately maintain each cat for a few days, then allow them to re-introduce themselves to each other and settle their own territorial disputes.