Everything is immortal until it encounters a mortal wound.
By everything, of course, I consider the image of multi-cellular organisms as "kingdoms." If the population of a kingdom is low enough, it will starve because it cannot provide enough food and protection of its people. If all the members of the kingdom are immortal and do not suffer wounds, then the kingdom is immortal. We are not a thing but a collection of things that work together for the survival of the whole organism.