Read the following passage and answer the questions given below:

The debate between the Neorealists and the Neoliberals emerged in the 1970's and developed over the next two decades into the major theoretical controversy within IR. Waltz himself contributed to the classical brand of Realism with his 'Man, the State and War' (1959) which echoed Morgenthau's and Carr's treatment of IR as a never-ending series of conflicts among states trapped in a condition of anarchy. Twenty years later, Waltz published his theory of International Politics (1979) in which he sought to explain the causes of wars. The structural realism is captured in the concept of the balance of power. This system is where we need to focus our attention because its all constituent units perform the same functions in that system, regardless of where they are located in the system, their ideology and culture. Waltz argues that bipolar systems are more stable than multipolar systems. According to him in international relations the idea of the system is all important.

According to Waltz what does he mean by system.