Failures to bring internationalised civil wars, such as in Syria, Libya, or Yemen, to a negotiated agreement have led to a questioning of the UN's role in peacemaking. The literature explains such mediation outcomes by examining micro-level aspects pertaining to either the mediation process or the conflict context. While both are important, they are influenced by macro-level dynamics related to world politics that have received less attention. Yet, such an awareness of the structural context in which mediation takes place is particularly relevant in times of tectonic shifts in world politics, such as the current change in world order from unipolarity to multipolarity. This article fills this gap by exploring the mechanisms through which macro- and micro-level factors interact in mediation, illustrated by the case of the UN mediation in Syria. The article thereby makes two contributions. First, it provides an analysis of the link between world politics and UN mediation by complementing micro-level explanations with a macro-level perspective. Second, it allows for a better understanding of UN mediation in internationalised civil wars, and particularly in Syria. Overall, the article contributes to reflections on how the UN can keep its relevance in peacemaking in a shifting world order.