In this article, I make a case for studying the outcome of security cooperation between external and host forces through the lens of their relationship. This is because in order for such military cooperation to have a sustainable effect, the host needs to develop ownership and autonomy over its own security responses. This article sets out from the observation that there is an evident discrepancy between the stated intent and the actual outcome of the cooperation between the G5 Sahel Joint Force (G5S-JF) and external actors. Building on insights from peace-building and security force assistance (SFA) literature, I argue that the relationship between the G5S-JF and external actors is best characterised as one of asymmetric interdependence and that this asymmetric interdependence can explain why the G5S-JF never developed into an autonomous force with ownership over its security responses. The concept of asymmetric interdependence provides a new lens through which to research SFA and can potentially shed light on other relationships between international, regional, national and local actors more generally.