This study applies the appraisal theory of emotions to explore how they influence leaders’ responses in the context of long-standing rivalries between states. It argues that policymakers’ emotions toward a rival country can help elucidate periods of higher and lower tensions in their bilateral relationship. Focusing on the Bolivian–Chilean rivalry, this study examines the case of Bolivia’s former president Evo Morales to shed light on the noticeable change in foreign policy toward Chile during two of his presidential terms. The findings reveal that Morales’s emotions were distinctly different during the period of cooperation or de-escalation compared to the period of escalation of tensions. The period of cooperation is characterized by strategies that promote contact, aligning with motive-consistent appraisals of events. Conversely, the period of escalation is marked by strategies that favor distance, stemming from motive-inconsistent appraisals.