Post-conflict interventions are often promoted for their presumed positive long-term influence on peace and justice. Concerns linger, however, that they can also let the state off the hook by replacing, and thereby undermining, its capacity over time. Unfortunately, scholarly research assessing the longterm influence of post-conflict interventions is rare, and practitioner evaluations are primarily shortterm processes regarding individual, temporally bounded projects. This paper explores the potential of, and challenges to, coordinated ethnographic peace research for assessing the longer-term influences of post-conflict interventions writ large on state capacity. A key challenge is identified in the complex interactions between projects implemented a) in parallel, b) at different scales, and/or c) in different time periods; which together mean that any influence observed may be overdetermined and hard to link back to a specific peace or justice project. But, as will be argued, coordinated ethnographic peace research provides hope of overcoming these challenges.