I think starting a war is very rarely justified. The evil prevented by attacking would need to be much larger than the inherent evil of the war. That’s pretty close to Justinian just war theory, but I’d weight present known evils much more highly than theoretically reduced future evils to account for uncertainty. For example, I think an allied invasion into Nazi Europe was justified.
Russia’s invasion is totally unjustified.
I think starting a war is very rarely justified. The evil prevented by attacking would need to be much larger than the inherent evil of the war. That’s pretty close to Justinian just war theory, but I’d weight present known evils much more highly than theoretically reduced future evils to account for uncertainty. For example, I think an allied invasion into Nazi Europe was justified.