What is the psychology behind being territorial?

Personal space acts as protection, a safety device, and a status marker. Dominant animals maintain a larger buffer zone of personal space, they are not approached as closely as submissive animals. When people stand too close, their faces become visually distorted. Personal space may vary in size for an individual depending on the situation, his or her emotional state, gender, and the relationship with the other person. We stand closer to people whom we like. Sometimes people erect actual boundaries to stake a claim to their personal space. Leaving an occupied sign on an airplane seat, draping a coat over the back of a chair in a restaurant, arranging a towel and sunscreen on a hotel poolside lounge, or spreading books across a library desk indicate this place is mine, and I will be returning to claim it—so keep off! People often mark where their territory begins or ends. A fence may separate one yard from that of a neighbor, just as painted lines demarcate parking spaces, and the bedroom door clearly delineates that area from the rest of the residence.

All societies have some way of recognizing private spaces and punishing those who do not respect the boundaries of these spaces, and this has been true throughout human history. Ancient Romans even had a deity named Terminus, who was the god of land boundaries. Anyone who tampered with these stones was punished harshly according to both civil and religious laws. Feelings of ownership increase with time, research consistently shows that people develop a sense of ownership over places where they spend a lot of time, and the intensity of our feelings increases with the time we spend there. Territories help us preserve and manage privacy, having a place where we can control who has access to us and when is essential for normal day-to-day functioning, and a lack of such control can be quite dispiriting and stressful. Territories also communicate personal identity, territories allow people to manage and communicate their sense of who they are. Territoriality organizes day-to-day life, territoriality also plays a crucial role in organizing everyday social life, without coherent ownership and control over various spaces, human interaction would be chaotic. Territories clarify social roles, regulate interaction, and minimize conflict.