Explain why some Christians believe that acts of terrorism can never be regarded as a 'Just War'?

Question

Please refer to Thomas Aqinas' Just War Theory

Answer 1

"The mere fact that war has regrettably broken out does not mean that everything becomes licit between the warring parties." (St. Thomas Aquinas, STh II-II, 158, 1 ad 3)

The “just war” doctrine requires rigorous consideration to determine if defense by military force is legitimate.

Offensive war is never justified.

All the following considerations must be true to justify war:
1. The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
2. All other means of putting an end to it must have been shown to be impractical or ineffective;
3. There must be serious prospects of success;
4. The use of arms must not produce evils and disorders graver than the evil to be eliminated.

By targeting innocent civilians, terrorism would violate the 4th clause.

With love in Christ.