Full Idea
Wars can be unjust despite having a just cause, because they are not actually needed, or they will cause excessive harm, or they also pursue some unjust causes.
Gist of Idea
Wars can be unjust, despite a just cause, if they are unnecessary or excessive or of mixed cause
Source
Jeff McMahan (Killing in War [2009], 1.1)
Book Reference
McMahan,Jeff: 'Killing in War' [OUP 2009], p.5
A Reaction
[compressed] The point is that older writers often think that a 'just cause' is sufficient. He is obviously right.