78 CHAPTER THREE ■ InternatIonal relatIons theorIes
realists agree on what they are. For example, six centuries after Thucydides lived, the
Christian bishop and phi los o pher Saint Augustine (354–430) added a fundamental
assumption of realism, arguing that humanity is flawed, egoistic, and selfish, although
not predetermined to be so. Augustine blames war on these basic characteristics of
hu ma n it y.^4 Although subsequent realists dispute Augustine’s biblical explanation for
humanity’s flawed, selfish nature, few realists dispute the fact that humans are basi-
cally power seeking and self- absorbed.
The central tenet virtually all realist theorists accept is that the chief constraint on
“better” state be hav ior— especially enduring peace—is that states exist in an anarchic
international system. This tenet was forcefully articulated by Thomas Hobbes (see Chap-
ter 1), who lived and wrote during one of history’s greatest periods of turmoil (the
Thirty Years’ War, 1618–48, and the En glish Civil Wars, 1641–51). Hobbes maintained
that just as individuals in a hy po thet i cal “state of nature” have the responsibility and the
right to preserve themselves— including a right of vio lence against others—so too
does each state in the international system. In his most famous treatise, Leviathan,
Hobbes argued that the only cure for perpetual war within a state was the emergence
of a single power ful prince who could overawe all others: a leviathan. Applying his argu-
ments to relations among sovereigns, Hobbes depicted a condition of anarchy where
the norm for states is “having their weapons pointing, and their eyes fixed on one
a not her.”^5 In the absence of an international sovereign to enforce rules, few rules or
norms can restrain states. War— defined by Hobbes as a climate in which peace cannot
be guaranteed— would be perpetual.
In sum, by the twentieth century, most of the central tenets of realism were well
established. Given a system in which no single power was capable of imposing its
will on all the others (anarchy), states in the system had to rely on self- help. Because
even allies might, in a crisis, hesitate or refuse to come to an ally’s aid, a state’s only
rational policy in a self- help world would be to seek power. According to one promi-
nent post– World War II realist, international relations theorist Hans Morgenthau
(1904–80), this idea explained why peace in the inter national system would always
prove elusive.
realism in the twentieth and twenty- first centuries
In the aftermath of World War II, Morgenthau wrote the seminal synthesis of real-
ism in international politics and offered what he argued was a methodological
approach for testing this theory. For Morgenthau, just as for Thucydides, Augustine,
and Hobbes, international politics is best characterized as a strug gle for power. That
strug gle can be explained at the three levels of analy sis: (1) the flawed individual in
the state of nature strug gles for self- preservation; (2) the autonomous and unitary
state is constantly involved in power strug gles, balancing power with power and react-