This paper deals with the causes of the dynamic change between German-American cooperation in the case of Afghanistan and conflict in the case of Iraq. It argues from a mainly theoretical perspective inspired by critical realism that the German-American security relationship is driven by the dialectic interplay of agential, structural, ideational and material factors and two connected dilemmas which emerge from it: On the agential side, humans are confronted with the dilemma of existential loneliness out of which the pursuit of both friendly love and power emerge. But because love between friends is based on shared ideas, differing ideas result in frustrated love and the drive for power. On the structural side, humans face the dilemma that different ideas emerge from differences in materially based social positions. In combination, these two dilemmas lead to crisis-tendencies which cause conflict when they are not counteracted by reflective agents wishing to cooperate.