A variety of factors promote group cohesion. These include shared goals that have emotional significance to group members, as well as a history of success in reaching those goals. Leadership styles are also important. Effective leaders attend both to the goals of the group and to the social and emotional needs of the group. Finally, opposition to or contrast with an out-group can also promote group cohesion. In some cases, this can be harmless or even beneficial, as with rivalry between sports teams. However, this tendency can also have negative implications as groups can demonize out-groups or escalate inter-group tensions in an effort to promote group cohesion. This can take the form of racism, prejudice, or even wars.