The Euro-Maidan in Ukraine, the annexation of Crimea and the Moscow-supported separatism in Donbas caused the deepest crisis in Est-West-relations after 1989/90. Interpretations of the conflict are hard faught. What did the actors learn? The confrontation with Russia is rooted in fundamental conflicts of values and interests, which overshadow any return to trustworthy relations. Some politicians opt for détente, others for deterrence. What are the lessons learned for security policy, conflict prevention and crisis management?