Power corresponds to the human ability not just to act but to act in concert. Power is never the property of an individual; it belongs to a group and remains in existence only so long as the group keeps together. When we say of somebody that he is “in power” we actually refer to his being empowered by a certain number of people to act in their name.

Hannah Arendt (1906-1975) German-American philosopher, political theorist

On Violence, ch. 2 (1970)
    (Source)

This book is an expansion of her essay (1969-02-27) "Reflections on Violence," The New York Review of Books; this passage is not in the original.