Based on evolutionary theory, Bauer, Henrich, and colleagues hypothesized that experiences with intergroup conflicts should lead individuals to become more focused on their own group's well - being, since individual survival is often linked to the fate of the group. (sciencedaily.com)
As they begin to lose comrades, the fate of the group becomes unclear, more so when they gain new locales and, with them, new conflicts. (rottentomatoes.com)