John Mearsheimer

Security competition is endemic to daily life in the international system, but war is not. Only occasionally does security competition give way to war

One might surmise that international anarchy is the key structural factor that causes states to fight wars. After all, the best way for states to survive in an anarchic system in which other states have some offensive capability and intentions that might be hostile is to have more rather than less power.

international system is usually arranged in three different ways: bipolarity

balanced multipolarity, and unbalanced multipolarity

he problem is that anarchy is a constant—the system is always anarchic—whereas war is not. To account for this important variation in state behavior, it is necessary to consider another structural variable: the distribution of power among the leading states in the system. As discussed in Chapter 8, power in the

sum, both geography and the distribution of power play a key role in determining whether threatened great powers form balancing coalitions or buck-pass against dangerous aggressors

Regarding multipolarity, the theory predicts that buck-passing is most likely in the absence of a potential hegemon but still likely to occur even when there is an especially powerful state in the system

The core of my argument is that bipolar systems tend to be the most peaceful, and unbalanced multipolar systems are the most prone to deadly conflict. Balanced multipolar sytems fall somewhere in between

Structural theories such as offensive realism are at best crude predictors of when security competition leads to war. They are not capable of explaining precisely how often war will occur in one kind of system compared to another. Nor are they capable of predicting exactly when wars will occur

Some of those theories treat human nature as the taproot of conflict, while others focus on individual leaders, domestic politics, political ideology, capitalism, economic interdependence, and the structure of the international system. In fact, a handful of prominent theories point to the distribution of power as the key to understanding international conflict