UN peacekeeping was not designed to wield force, and the UN's permanent five (P-5), veto-wielding Security Council members do not want the UN to develop a military capacity. However, since 1999, the UN Security Council has authorized all UN multidimensional peacekeeping operations under Chapter VII of the UN Charter to use force. The mandates do not serve to achieve the council's stated goal of maintaining international peace, nevertheless, the council repeats these mandates in every multidimensional peacekeeping resolution. Neither constructivist accounts of normative change, nor the rational pursuit of stated goals, nor organizational processes can explain the repetition of force mandates. Instead, we draw on insights from small-group psychology to advance a novel theoretical proposition: the repetition of force mandates is the result of “group-preserving” dynamics. The P-5 members strive to maintain their individual and collective status and legitimacy by issuing decisions on the use of force. Once members achieve a decision, the agreement is applied in future rounds of negotiations, even when the solution does not fit the new context and may appear suboptimal, illogical, or even pathological. Privileging the achievement and reproduction of agreement over its content is the essence of group preserving. We present an original data set of all peacekeeping mandates, alongside evidence from dozens of interviews with peacekeeping officials, including representatives of all of the Security Council's permanent members. We assess this original data using expected causal process observations derived from rationalist, constructivist, organizational, and psychological logics.