statehood with great difficulty. But let us begin with the strong side of structural
realism, balance of power analysis.^5
Unipolarity and the balance of power
It is sometimes forgotten that structural realism is not a theory about everything, a
point explicitly emphasised by Waltz.^6 It does not primarily aim to explain the
demise of the Soviet Union, the emergence of international terrorism, or even the
foreign policy of a certain state. Structural realism is a systemic theory about the way
in which the systemic pressures expressed through the balance of power constrain
the behaviour of states. Whatever change there may have been, structural realism
emphasises basic continuity as regards the international system: it remains a system
of independent political units with no central authority above them; therefore, the
system is anarchic. States want to survive and take measures to defend themselves.
But in a self-help system, ‘many of the means by which a state tries to increase its
security decrease the security of others’^7. This is the security dilemma; states face it
through instrumentally rational behaviour; they ‘think strategically about how to
survive in the international system’.^8
Two basic options are available to states seeking security: preparing for self-
defence and/or seeking security-enhancing alliances with others. Since most states
face limitations in providing for self-defence, appropriate alliance strategies become
crucially important. In this game, states are constrained by the distribution of power
in the international system and the existing place of a given state within that
distribution. That is because differences of power – the relative distribution of
capabilities – is the most decisive determinant of state behaviour:
In a self-help system, states are differently placed by their power. States are
self-regarding units. State behaviour varies more with differences of power
than with differences in ideology, in internal structure of property relations,
or in governmental form. In self-help systems, the pressures of competition
weigh more heavily than ideological preferences or internal political
pressures.^9According to structural realism, then, the pressures of competition depend on
the distribution of power. In a bipolar system, with two leading states significantly
more powerful than any of their competitors, these two states are compelled to be
rivals. Lesser states will seek the alliance that offers maximum security and freedom
of action. Systemic constraints on states are at their strongest when state survival and
autonomy are at stake:
Realism can offer its most precise explanations when states have few options
because they are narrowly constrained by the international distribution of
power. Britain was bound to balance against Germany in both the First and
Second World Wars because Germany was the one state that had the potential108 Structural realism and changes in statehood