Balance of power is a concept in International Relations that refers to the distribution of power and resources among states in the international system. The balance of power refers to a situation in which no one state is dominant and all states have roughly equal power and influence. The concept of balance of power has been used to explain the behavior of states and to analyze the stability of the international system. According to this theory, states will work to maintain the balance of power by aligning with other states, forming alliances, and pursuing policies that counter the power of dominant states.
Source: Waltz, K. N. (1979). Theory of International Politics. Reading, MA: Addison-Wesley.