Realism (and Neorealism) 77can rely only on themselves. Their most impor tant concern is to increase their own
relative power. They can do so by means of two logical pathways: (1) war (and con
quest) or (2) balance ( either dividing the power of real or potential rivals by means of
alliance politics or economic sanctions, or multiplying their own power by raising
armies, or manufacturing fearsome weaponry).
the roots of realism
At least four of the essential assumptions of realism are found in Thucydides’s History
of the Peloponnesian War.^3 First, for Thucydides, the state (in this case, Athens and
Sparta) is the principal actor in war and in politics in general, just as today’s realists
posit. Although other actors, such as international institutions, may participate, their
impact on the system is marginal.
Second, the state is assumed to be a unitary actor. Although Thucydides includes
fascinating debates among dif er ent officials from the same state, he argues that once
a state decides to go to war or capitulate, it speaks and acts with one voice. No subna
tional actors are trying to overturn the government’s decision or subvert the state’s
interests.
Third, decision makers acting in the name of the state are assumed to be rational
actors. Like most educated Greeks, Thucydides believed that individuals are essentially
rational beings who make decisions by weighing the strengths and weaknesses of vari
ous options against the goal to be achieved. Thucydides admitted that potential imped
iments to rational decision making exist, including wishful thinking by leaders,
confusing intentions and national interests, and misperceiving the characteristics of
the counterpart decision maker. But the core notion— that rational decision making
leads to the pursuit of the national interest— remains. Likewise for modern realists,
rational decisions advance the national interest— the interests of the state— however
ambiguously that national interest is formulated.
Fourth, Thucydides, like con temporary realists, was concerned with security
issues— the state’s need to protect itself from enemies both foreign and domestic. A
state augments its security by increasing its domestic capacities, strengthening its eco
nomic prowess, and forming alliances with other states based on similar interests. In
fact, Thucydides found that before and during the Peloponnesian War, fear of rivals
motivated states to join alliances, a rational decision by their leaders. In perhaps the most
famous section of History of the Peloponnesian War, the Melian dialogue, Thucydides
summarized a key tenet of realist thinking: “[T]he strong do what they can and the
weak sufer what they must.” More generally, do states have rights based on the con
ception of an international ethical or moral order, as liberals suggest? Or is a state’s
power, in the absence of an international authority, the deciding factor?
Thucydides did not identify all the tenets of what we think of as realism today.
Indeed, the tenets and rationale of realism have unfolded over centuries, and not all