This two part thesis investigates the lack of definition of the wording “all necessary means” and how it ultimately impacts a decision making gap between the Security Council and the troop contributing countries regarding the use of force in UN peace operations. The assumptions are based on Reus-Smit’s constructivist theory, emphasizing that both politics and international law needs to be studied with a holistic approach in order to understand how the two realms shape each other. The assumption of this thesis is that “all necessary means” is not providing enough guidance to constrain the TCCs to behave as sovereign, equal actors in an anarchical structure. The second part of the thesis is a within-case-study of MONUC/MONUSCO, and the Security Council resolution 2098 that established the Force Intervention Brigade.