Christian Peace Ethics and the War in Ukraine: On the Relevance of the Doctrine of Just War. Putin’s war against Ukraine has ended a 30-year- old period of European history and he has thrown the peace ethics of catholic and protestant theologians into confusion. They were convinced that the doctrine of just war was succeeded by the concept of just peace. But Putin’s war has made it clear that the narrative of just peace is not suitable for replacing the doctrine of just war and that Christian peace ethics has to discuss openly the concept of nuclear deterrence. The concept of nuclear deterrence belongs to the «prudential judgements», not to the principles regulated in the Catechism of the Catholic Church.