Palestinians resisting the Israeli occupation and black Americans protesting state violence in the United States are examples of historically disadvantaged groups seeking to overcome prolonged oppression and injustice. Both groups sometimes engage in collective action along with allies from the advantaged group. This joint action may have considerable potential to promote social change, but there is a need to understand when the disadvantaged will be willing and motivated to participate in such action. While research has given us rich descriptions of the motivations of disadvantaged group members to act collectively with other members of their group (ingroup action, see Van Zomeren, Postmes, & Spears, 2008) and the motivations of advantaged groups to act on behalf of the disadvantaged (solidarity based action, see Saab, Tausch, Spears, & Cheung, 2015; Van Zomeren, Postmes, Spears, & Bettache, 2011), it is unclear if these motivations also apply to joint action. Indeed, joint collective action requires members of the disadvantaged group to negotiate between intergroup tension and harmony, that is, between the orientation to characterize the outgroup as the oppressor and the orientation to soften intergroup disparity and accept outgroup members as allies (see Saguy,