Gianluca Grimalda presenting his work titled “Sanctions and International Interactions Improve Cooperation to Prevent Collective Losses” The use of sanctions is often invoked to bolster international agreements. For instance, it has been proposed to link lack of compliance to climate change agreements with trade sanctions. We investigate experimentally whether sanctions may improve international cooperation.Participants are involved in “collective risk social dilemmas” (CRSDs), where group members are faced with the possibility of collective losses at the end of the game and can cooperate to reduce the risk of such an event. We sample German and Russian pools because previous research found significant cultural differences in their ability to use sanctions to increase cooperation. We find that in international interactions with sanctions Russian participants cooperate significantly more than in national interactions, while German participants cooperate at the same level as in national interactions. Russians’ cooperation levels quickly converge towards Germans’ cooperation levels internationally, while Germans cooperate significantly more than Russians nationally. Without sanctions, cooperation by Russians does not significantly increase internationally in comparison with national interactions. Revealing group members’ nationality leads to the same results as not revealing nationality. These results suggest that norms of behavior are malleable to the observation of counterparts’ behavior, and that societies may get trapped into equilibria characterized by mutual diffidence and low cooperation. International interactions seem to easily unlock such diffidence traps, when more cooperative groups are mixed with less cooperative groups.