UN peacekeeping missions are typically assessed in terms of security provision and mandate implementation, yet they also function as major economic and governance actors. In South Sudan, UNMISS operates not only as a protection force but as an employer, purchaser, infrastructure provider, and, at times, a practical competitor to state institutions. This study examines how peacekeeping-mediated political economy shapes political order from independence through the civil war period to recent mission restructuring, with comparative reference to MONUSCO and AMISOM/ATMIS. Drawing on critical peacekeeping studies, the local political economy of peace operations, and humanitarian economy analysis, the study combines budget and procurement analysis with labour market inquiry, interviews with mission personnel and local stakeholders, and cross-mission comparison. The findings show that peacekeeping economies are not neutral or temporary but generate durable effects by reshaping incentives, authority, and access to resources (Pouligny 2006; Whitworth 2004; Higate & Henry 2009; Jennings 2015). UNMISS influences wage structures, local markets, and service provision in ways that can both stabilise livelihoods and displace state functions. Variation across missions reflects differences in mandate scope, resource scale, and host-state capacity. The contribution lies in demonstrating how peacekeeping missions become embedded in domestic political economies, affecting governance outcomes beyond their formal mandates. It argues that more effective reform requires aligning mission design with local institutional development and addressing the economic and political effects of large-scale external presence (Carbonnier 2014; Bellamy & Williams 2013; UNMISS 2024; Cuddington & Langford 2017).