peacekeeping, V. Page Fortna finds that peacekeepers
reduce the risk of subsequent fighting between former
belligerents from 50 percent to 75 percent, noting that
the effect may even be stronger as peacekeepers often
deploy to difficult conflicts where stability is harder
to obtain.19 Other studies reach similar conclusions.
After adjusting for the non-random deployment of
peacekeepers through matching, Michael Gilligan and
E.J. Sergenti show that UN peacekeeping operations
reduce the risk of conflict recurrence by 85 percent if
deployed at the end of the conflict.20 Another study
finds that peacekeepers reduce the risk of any new
civil conflict—either between the former belligerents
or new opponents—by approximately 70 percent.21
Conclusions about the effectiveness of peacekeeping in lengthening peace duration are based on comparison with the polyglot category of “no peacekeeping.” Most often, this does not include what may have
occurred if the conflict continued or at best lumps
such a scenario together with all others that do not
involve peacekeeping, thereby obscuring individual
effects. More specific analyses of non-intervention are
required to compare the outcomes with those involving peace operations. In her studies on peacekeeping,
Fortna also notes that decisive military outcomes tend
to improve stability. Compared to a cease-fire or truce,
having a clear winner reduces the risk of renewed violence by at least 85 percent while ending a war with a
peace agreement has a smaller effect (a reduction of
about 60 percent).22
A closer examination of war outcomes presents
some additional, more nuanced findings, suggesting that the impact of letting the fighting continue is
conditional on the final victor in the conflict. Michael
Quinn, David Mason, and Mehmet Gurses stress a
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