As the realist paradigm of International Relations holds, the development of the sovereign state itself determined the very nature of the Westphalian system: anarchical. Anarchy means the lack of a central authority or world government to enforce rules in the modern international system. In the absence of a higher authority, each actor seeks to ensure its own survival and mobilize all resources at its disposal to this effect.

The hierarchy within the evolving Westphalian system has emerged as a kind of an “invisible hand” which ensures the system consisting of political units, legally equal but varying in material capability, all operating in an equilibrium and maintaining their own continuity without the intervention of a central regulatory authority.

Balance of power implies equilibrium among competitors. It requires states to combine resources to ensure their survival as well as to maximize their interests in the international system. Does the combination of these resources depend upon the ability of a single political unit? To the contrary.  Its stability relies largely upon the similar behavior of other political units. A state tries to match the power of others to maintain the balance of power; for its own survival, the state needs to protect itself against another state (or group of states) and deter any potential threat to its own security.

States, therefore, form a counterbalancing alliance against common threats that they perceive from another state or coalition of states. This is the basic logic behind the balance of power in the international system. In fact, the balance of power mechanism has managed to prevent the total collapse of the international system.  It has converted great-power rivalries into a state of deterrence (or even of cooperation) when needed. As understood from the information given the correct answer is E.

Other concept "hegemony" which takes place in one of the options refers to a situation in which a powerful state or a coalition of powerful states shapes the international system through a set of coercive and non-coercive instruments.