Dogs can become overprotective for any number of reasons. Having a new baby in the family is one instance when a dog can feel the need to keep everyone safe. Why wouldn’t he try to protect such a valuable commodity from other dogs and people?
Whatever the reason that your dog overprotective nature developed, it’s something that you need to curb before it gets out of control. Left unchecked, this behaviour can lead to more serious aggression, and no one wants that for their dog.