Six studies explored the mechanisms that diminish allegiance to social groups. Results showed that degrading either collective ties (i.e., sentiments toward the group as a whole) or relational ties (i.e., sentiments toward individual group members) lowered identity fusion with the group (Studies 1–3 & 6). Lowered fusion, in turn, explained the tendency for weakened collective and relational ties to reduce endorsement of pro-group action, and this effect replicated cross-sectionally and longitudinally (Studies 2, 4 & 6). Additional evidence revealed that attenuated group-related agency seemed to mediate the relationship between weakened identity fusion and diminished commitment to help the group (Studies 3, 4 & 6). Although degrading collective ties reduced overall group identification (Studies 1–3 & 6), degrading relational ties did not reliably do so (Studies 1–6). Instead, degrading relational ties only reduced scores on a single component (ingroup solidarity) of a multidimensional measure of group identification (Studies 5 & 6). Hence, measures of identity fusion are equally sensitive to relational and collective ties while measures of identification emphasize collective ties. The results replicated whether we considered country (Studies 1–5) or gender (i.e. females, Study 6) as the focal social group. These findings therefore highlight the unique properties of fusion and identification and help explain why identity fusion predicts extreme pro-group behavior with greater fidelity than group identification.