Members of groups in conflict may take collective action: actions to improve conditions for their group as a whole. The psychological antecedents of collective action for groups that are party to conflict and inequality are well-established. Comparatively little is known about how uninvolved outsiders respond to an external intergroup conflict. We investigate how personal ideological orientations of Social Dominance Orientation (SDO) and Right-Wing Authoritarianism (RWA) shape outsiders' willingness to take collective action in support of groups engaged in external conflict. In Study 1, U.S. residents read about conflicts between disadvantaged citizens and an advantaged government in Greece and Russia. In Study 2, U.S. residents read about a similar conflict in a fictional country, Silaria. Path analyses revealed that SDO and RWA shaped psychological appraisals of the conflict contexts, which predicted intentions to take collective action on behalf of either group. SDO and RWA were positively associated with advantaged group identification and anger at a disadvantaged group, and negatively associated with disadvantaged group identification and anger at an advantaged group. Group identification and anger predicted subsequent collective action intentions on behalf of either group. The sensitivity of outsiders' appraisals to ideological orientations suggests strategies for both advantaged and disadvantaged groups to recruit outsiders as allies in group conflict.