  According to Waltz, the uniform behavior of states over centuries can be explained by the constraints on their behavior that are imposed by the structure of the international system. A system’s structure is defined first by the principle by which it is organized, then by the differentiation of its units, and finally by the distribution of capabilities (power) across units. Anarchy, or the absence of central authority, is for Waltz the ordering principle of the international system. The units of the international system are states. Waltz recognizes the existence of non-state actors, but dismisses them as relatively unimportant. Since all states want to survive, and anarchy presupposes a self-help system in which each state has to take care of itself, there is no division of labor or functional differentiation among them. While functionally similar, they are nonetheless distinguished by their relative capabilities (the power each of them represents) to perform the same function.