Integrating theory on distinct modes of social identity (Roccas, Sagiv, Schwartz, & Eidelson, 2008) with group-based emotion in protracted conflict (Halperin & Pilskin, 2015) and exposure to outgroups (Saguy & Halperin, 2014), this dissertation tests how Jewish Israelis respond when ingroup members and outgroup members work together to advocate for peaceful solutions to conflict (i.e., intergroup solidarity), and how glorification of one’s national group moderates these responses. Instructing participants to imagine a peace activist organization, Study 1 shows evidence that glorification of one’s ingroup predicts more anger, less hope, and less support for a political solution reflecting compromise. With a student sample, Study 2 shows that learning about an activist organization where both groups work together, relative to an organization where ingroup members work alone, increases support for allowing the organization to present on campus by reducing anger and increasing hope. Manipulating both group composition and the target of criticism, Study 3 shows that glorification becomes less predictive of negative responses to activism when the activist organization consists of only ingroup members, and when both ingroup members and outgroup members are criticized for their role in the conflict.