Which type of aggression involves a dog that reacts to protect its territory?

Territorial aggression is characterized by a dog's instinctual need to protect its home or territory from perceived intruders. This behavior can manifest when a dog feels that its space is being invaded, and it may become defensive or aggressive towards anything or anyone it deems a threat within that area. The motivation behind this type of aggression is deeply rooted in the dog's natural instincts to safeguard its living environment.

On the other hand, dominant aggression is often based on a social hierarchy, where the dog is asserting its position over others. Possessive aggression involves protecting a specific resource, such as food or toys, rather than an area. Punishment aggression is a reaction to an adversive experience, often directed at a person who has punished the dog. While these types of aggression can overlap, territorial aggression specifically pertains to an instinct to defend a defined geographical space, making it the appropriate answer to the question.