Cats have an instinct to stake out and mark territory. This behavior is more prominently shown in unneutered males and dominant cats in a household; however, all cats can display territorialism. Make sure your cat has his/her own things (especially if you have multiple cats). Each cat should have his/her own toys, beds, areas to sleep and rest in etc. Cats who do not feel that they have enough territory or feel that their territory is threatened can show aggressive behaviordominance behavior or spraying. A classic example of this is the indoor cat who, by looking out through the window, starts to see an outdoor cat in the yard. Your indoor cat may start acting territorial (spraying etc.) after seeing the new cat. Cats can show territorialism in the following way:

If you find that your cat is exhibiting problem behaviors you can minimize that behavior by helping your cat to reduce his territorial instinct/need for territorialism. You can do this by keeping your kitty in an environment where he/she feels safe and comfortable, keep unwanted ‘intruders’ out of the home or out of sight, and make sure he/she has plenty of food, water and territory to call his/her own. Also if you have multiple cats stick to the established hierarchy that your cats have set up. Always treat your dominant cat as the dominant head of household. Also make sure to spay/neuter all of your cats, not only to reduce territorialism but to keep him/her happy and healthy in the long run.