Mearsheimer's innovate concept of "unbalanced multipolarity". Waltz has focused his study on the stability of the bipolar system, but neglects a detailed explanation of the unipolar system. Mearsheimer's integrates the basic neo-realists assumptions to his own theories, and tends to describe better the international system.
Waltz was the first to employ the term "polarity" in order to describe the structure of the world. According to his assumption, the bipolarity system with only two relatively equal superpowers is to be the most stable system because, "The two powers watch each other carefully, and neither can make gains without energizing intense balancing behavior by the other." Both Waltz and Mearsheimer agree that the multipolarity system is stable when states are equal in power and no one is significantly capable to dominate others. However, it still unstable compared to the bipolar system: "though it may be characterized by much diplomatic jockeying for advantage and some war, large-scale war should not occur." Furthermore, Mearsheimer points out that a multipolarity structure is not always balanced, when powers between states are not relatively equal, stronger powers are usually tempted to buck pass rather than balance. This leads an unbalanced multipolarity situation where one state increases its security by decreasing the other's security. Hence, war is easily assessable. At last, unipolarity is the least stable of all structures from a neo-realist point of view. The great concentration of powers by a single state threatens other states, and causes them to take action to restore the balance. .
A significant contrast exists between Waltz (defensive realism) and Mearsheimer (offensive realism) theory of international systems. Waltz argues that "despite the condition of anarchy, states will stop well short of hegemony if geography or technology or social organization favors the defense.
