Evolutionary theory maintains that intergroup conflict leads to increases in intragroup cohesion.

According to evolutionary theory, intergroup conflict can lead to increases in intragroup cohesion as individuals within a group may come together for protection, support, and cooperation in order to compete with other groups for resources or survival. This idea is known as the "group selection" hypothesis which implies that groups that are more cooperative and cohesive have an advantage over those that are not, leading to the evolution of behaviors that promote cooperation and group cohesion.