When the rebel group FARC started to govern the rural communities of Santa Rosa and Buenavista in central Colombia in the 1990s, both communities thought the rebels to be legitimate. Yet, by the mid-2000s, despite similar dynamics of FARC governance, the two communities differed in their legitimacy beliefs towards the FARC: Buenavista was still supportive of the rebels, but Santa Rosa was no longer. What explains local variation in the legitimacy of armed actors during civil war? Existing scholarship fails to account for such variation as it pre-specifies ‘sources of legitimacy’, considers beliefs about rightful rule as static and sees legitimation as isolated from network dynamics. Conversely, this thesis argues that civil wars are contexts of complex governance networks, where civilians are confronted with different armed actors’ governance simultaneously over time. Legitimation should therefore be understood as a process of congruence-finding, an aligning of the normative beliefs of ruler and ruled, with more congruence giving rise to stabler governance practices. These normative beliefs can change through network mechanisms both within and across governance relations. Combining process tracing with four months of immersive fieldwork in central Colombia, the thesis tests this theory of legitimation with a most-similar case design of the rural communities of Buenavista and Santa Rosa. Local variation in the legitimacy of the FARC, it finds, cannot be explained by dynamics within the relation between the FARC and each community but by network effects, particularly the role of the state in Buenavista. The thesis pushes forward our understanding of the relationship between legitimation processes and governance networks by (a) offering a theory of congruence-finding that can capture and explain legitimation dynamics in complex governance networks; (b) specifying several mechanisms of how beliefs change endogenously to governance networks; and (c) contributing to the link between rebel governance and (self-)legitimation and its significance for the Colombian conflict.