The thesis that unipolarity is not a peaceful international system structure is grounded in the structural realism theory of international relations, as articulated by Mearsheimer and Walt. Structural realism, also known as offensive realism, rests on five key assumptions. First, states are the principal actors in the international system. Second, the international system is anarchic—there is no central authority governing state behavior. Third, while all states possess some military capability, some are more powerful than others, and military power is the most important measure of state strength. Fourth, states can never be certain of each other’s intentions, especially future intentions. Finally, all states seek survival as their primary goal, without which no other objectives can be pursued. States are assumed to be rational actors that act strategically to secure their national interests (Mearsheimer, 2001).
These assumptions produce three key patterns of behavior among states. First, all states aim to maximize the power they control. Second, states inherently fear one another, although the degree of fear varies depending on their capabilities and vulnerabilities. Third, states recognize that they operate in a self-help world where no higher authority can guarantee their security.
Under structural realism, great powers pursue two central goals. The ultimate goal of any great power is to become a regional hegemon, as this is the best way to ensure its long-term survival. The second goal is to prevent other states from becoming regional hegemons, as potential peer competitors could threaten their dominance and security (Mearsheimer, 2001).
This theoretical framework underpins the argument that unipolarity is not a peaceful system. While structural realism acknowledges that unipolarity may reduce uncertainty and thus temporarily suppress great power conflict, it also introduces mechanisms that are inherently conflict-producing. Most importantly, the peacefulness of a unipolar system is contingent upon the foreign policy choices of the unipole. In the case of the United States, its interventionist foreign policy has not fostered peace but instead generated significant opposition and instability, accelerating the shift toward a bipolar or multipolar system.
Unipolarity fosters conflict in multiple ways. It increases tensions between the unipole and subordinate states, and it can also provoke conflict between subordinate states themselves. It exacerbates global power imbalances, prompting other states to seek a restoration of equilibrium in pursuit of their own security and survival. These dynamics make unipolarity inherently unstable and conflict-prone.
Moreover, claims that unipolarity is peaceful suffer from two major limitations. First, they often focus narrowly on great power relations while ignoring conflicts involving weaker states. Second, they assume the unipole will pursue only defensive dominance, overlooking more aggressive or interventionist strategies that increase the likelihood of conflict. U.S. hegemony, for example, has involved numerous military interventions aimed at preserving global influence and preventing the rise of rival powers (Mearsheimer, 2001).
The erosion of unipolarity and the emergence of a more contested global order are, in part, a reaction to these dynamics. The U.S. foreign policy of interventionism has led to widespread conflict, growing resistance to its leadership, and declining legitimacy of international institutions tied to the unipolar order. In short, the realist international system suggests that unipolarity is not peaceful because it increases power disparities, fosters insecurity among subordinate states, and produces conflict through the unipole’s strategic behavior.
In conclusion, peace in a unipolar system depends heavily on the foreign policy of the dominant power. In the case of the United States, its pursuit of interventionist strategies has undermined global stability, strengthened calls for a multipolar order, and contributed to the delegitimization of international institutions. According to structural realism, these outcomes are not anomalies—they are the predictable consequences of unipolarity in an anarchic international system.