In traditional just war theory there are two basic elements: an account of just cause and an account of just means. Just cause is usually specified as follows:

(1) There must be substantial aggression.

(2) Nonbelligerent correctives must be either hopeless or too costly.

(3) Belligerent correctives must be neither hopeless nor too costly.

Needless to say, the notion of substantial aggression is a bit fuzzy, but it is generally understood to be the type of aggression that violates people's most fundamental rights. To suggest some specific examples of what is and is not substantial aggression, usually the taking of hostages is regarded as substantial aggression while the nationalization of particular firms owned by foreigners is not so regarded. But even when substantial aggression occurs, frequently nonbelligerent correctives are neither hopeless nor too costly. And even when nonbelligerent correctives are either hopeless or too costly, in order...