Can they ever be justified? Of course.
If a nation is building up armies to launch an attack, and you know for sure that that's what they're doing, and their propensity to launch the attack is not affected by your propensity to preemptively strike them (an important point), and a preemptive strike will result in many fewer casualties than letting the attack happen, it's pretty justified.
In real life it's the certainty about a nation's intentions that's the bottleneck.
In an existential struggle the standards are likely lower, as the long-term costs of strategic disadvantage are much greater. |