Just like rebel groups attract and recruit individuals, these organisations also experiencedisengagement. This study explores causes of rebel disengagement and examines why rebelgroups see increased levels of disengagement. Based on theoretical arguments derived fromliterature on rebel group structure and dynamics, and disengagement. The theoreticalframework is based on different types of rebels, and I suggest two causal mechanisms to fiteither economically opportunistic or ideologically driven rebels. I hypothesise that militarysetbacks for rebel groups lead to increased levels of disengagement. Military setbacks anddisengagement are measured on the group level while the causal mechanisms are considered onthe individual level. The case selection follows an exploratory most-similar design to scrutinisethe degree in which disengagement varies. Using a structured focused comparison, thehypothesis is tested on three cases, JAS during 2016 and 2021 in Nigeria and al-Shabaab during2023 in Somalia. The source material consists of news and NGO reports, academic sources, andsemi-structured expert interviews. The findings support a relationship between militarysetbacks and disengagement, but that further nuance is required to explain the degree to whichdisengagement occurs.