The idea of balance of power initially envisaged
the
relations between two states (and, by extension, two
groups) as
comparable to a pair of scales, with the
possibility of intervention by a
third party either to
restore the equilibrium or to tip the balance in
favor
of one of the two. Later, the notion was extended, first
to
three states, then to an entire congeries of states,
poised against one
another, any substantial change in
the mass of one of the units requiring a
regrouping
amongst the rest if the equilibrium was to be main-
tained. All this has developed into a
wider theory of
international politics which makes the preservation of
the equilibrium an object (even sometimes the over-
ruling object) of policy for the purpose of preventing
the
indefinite expansion of a predominant member of
the system; and which, by
its regard for the diagram
of forces, tends to base foreign policy on
considerations
relating to power.
