In times of severe intergroup conflict, cross-national interactions are shaped by social categorization along national and moral dimensions. Yet, little is known about how these co-occurring identities jointly shape prosocial behavior. Across three studies (total N = 1178), we examined how shared nationality and moral position shape prosocial behavior during a real-world conflict (Studies 1 and 2) and a fictional intergroup conflict (Study 3). Moral positions reflected different moral values–judgments of war justification (harm/care) in Studies 1 and 3, and moralized responses to conflict behavior (loyalty/punishment) in Study 2. Using a crossed-categorization paradigm, participants played dictator games with interaction partners representing all four combinations of nationality and moral position: co-national with a shared moral position, co-national with a non-shared moral position, foreign national with a shared moral position, and foreign national with a non-shared moral position. Participants behaved more prosocially toward those sharing their moral position than toward those who did not, and toward co-nationals. These effects were additive rather than interactive. Across studies, the effect associated with shared moral position was larger than that associated with shared nationality, being approximately sixfold larger in the real-world context and nearly threefold larger in the fictional setting. Intergroup bias consistently increased with ingroup identification for morality-based, but not consistently for nationality-based identities. Differences in ingroup identification could not account for the stronger morality-based bias. Together, these findings suggest that, when multiple social categorizations are salient in cross-national contexts, shared moral positions represent an important basis for prosocial behavior alongside shared nationality.