This research was conducted with dissident political parties' supporters that were represented in the parliament of Turkey via 2015 parliamentary election. Using the Identity Fusion Theory, the study aims to explore the relations of people with local in-group (supporters of the supported political party) and extended in-group (citizens of the Republic of Turkey); and test the endorsement of extreme behaviors as fighting or sacrificing own life to save in-group members or improve the current conditions of in-group. Accordingly, data was collected from Republican People's Party (CHP; N = 320), Peoples' Democratic Party (HDP; N = 215), and Nationalist Movement Party (MHP; N = 150) supporters. There were significant group differences on study variables based on one's political party identity. Broadly, local in-group based socio-psychological processes were stronger in samples of HDP, MHP, and CHP supporters, respectively whereas extended in-group based socio-psychological processes were stronger in samples of MHP, CHP, and HDP supporters, respectively. Moreover, local in-group and extended in-group based socio-psychological processes were positively associated with each other in samples of CHP, and MHP supporters; but not associated in sample of HDP supporters. Identity fusion with local in-group indicated positive indirect (mediational) associations with endorsement of extreme behaviors for the sake of local in-group and extended in-group in three samples. The research findings complement the related literature, and present a relatively new theoretical approach to explain extreme pro-group behaviors.
Identity fusion theory, extreme pro-group behavior, local in-group, extended in-group