This source of intra-alliance solidarity rests on two obvious prerequisites. The
alliance leader must be strongly committed to preserving the relationship and
willing to expend the effort needed to keep its allies from straying. In particular,
if changes in the external environment alter the leader's desire for allies, then
this source of solidarity will not be available. The alliance leader must also be
significantly stronger than its potentially disloyal allies, so that it is able to bear
the additional costs of enforcing compliance.