The insistence of the return of violence in countries where the UN has intervened to promote peace has fuelled a debate about the effectiveness of international instruments for conflict resolution. This article reflects on the progress that these instruments were having in response to the recurrence of violence in light of what has been an approach to the concept of positive peace of Johan Galtung. From two case studies (Guatemala and Haiti) marked by changes in the discourse and practice of the United Nations that this approach inspired, it is argued that the UN instruments for peace would be so much more effective when they respect the author's proposal, not only with regard to results they intend to achieve, but also in the way positive peace is operationalised on the ground. Analyses − as difficulties in implementing more comprehensive, local and inclusive processes that would affect the promotion of more sustainable peace − also contaminate the mechanisms used to assess their effectiveness.