You say Iraq, I say Sierra Leone. You say Afghanistan, I say Former Yugoslavia. You say Libya, I say Ivory Coast.
If you are willing to look at a wide spread of evidence, the exchange about whether or not military action can improve matters should be quite a long one, looking at many different countries, both where it has taken place and counter-factual examples where military action did not take place or took place only very belatedly, such as in Rwanda.
So what does a systematic review of the evidence show?
As with any overall pattern, there are exceptions which is why any decision should be made with caution, thought and humility. But the weight of evidence from previous military interventions makes it reasonable to say that you think military intervention in Syria this time is right in part because the balance of evidence from the past is in its favour. And given that balance of evidence, it is not only those who support military action who should be nervous they are getting it wrong; those who oppose it should be willing to apply the same rhetoric about sleepless nights and the rest to themselves as to those they disagree with.
Patrick Johnston in a study of militant degradation and its effect on end of conflicts and violence finds positive results. His study systematically looked at 118 decapacitation [sic – I misread this the first couple of times] efforts across 90 insurgency campaigns. Unlike previous studies (with the exception of one), this looks at both decapacitation attempts that failed to hit their targets and successful ones. This allows us to draw causal inferences because it gives us appropriate counterfactuals.
Johnston finds that militant decapacitation increases the probability of defeating the insurgency by 33 percentage points (Table 3, Column 5). There are positive results for both the lethality of their attacks and their frequency as well…
Military action can, therefore, work to reduce violence. This study not only confirms but also refutes the alternative hypothesis: i.e., the idea that it inflames the population to the extent of having a tangible effect on the success of terrorism. [Anonymous Mugwump]