And it’s more important than ever that we try to prevent it in the first place.

Dunne calculates that spending about 56 billion over four years on a combination of these measures would lead to benefits on the magnitude of at least $606 billion. Among these benefits, the avoided deaths, injuries, and other conflict-related violence are perhaps the most compelling arguments for the use of available funds for prevention.

Given the high possible benefits of avoided carnage and relatively low costs, conflict prevention has a benefit-cost ratio of at least 11. This means that, when we frame it in economic terms so that it can be compared to other interventions, each dollar spent achieves benefits worth at least $11.

If conflicts do break out, the next stage is intervention. At this stage it will be impossible to avoid a significant part of the cost of conflict, and the intervention itself will also be more costly. The projected $100 billion cost of intervention includes better intelligence, economic sanctions, and aid, as well as most likely military intervention. This is nearly double the cost of preventing a conflict in the first place. Yet, with benefits of at least $606 billion, there are still large pay-offs. For each dollar spent, we can avoid conflict damage worth about $5, making intervention a cost-effective use of resources.

When conflicts end, what is needed for reconstruction is contingent on the nature of the conflict and the way that it ended. Most of the costs of conflict have already been incurred, but experience shows it is possible to speed recovery and reduce the risk of relapse into further violence. Particularly important are the legacy costs of the conflict, such as more general violence within the society. Post-conflict policies can be costly but are also cost-effective in preventing suffering and building up economies that provide new markets and raw materials.  According to research by former Copenhagen Consensus expert panel member and researcher Paul Collier, economic reconstruction reduces the risk of a renewed outbreak of conflict by 42 percent in 10 years.

The cost of post-conflict policies is higher than intervention at around $140 billion, and the benefits are also smaller at $404 billion. In total, it is estimated that each dollar will avoid at least $3 of conflict damage. While post-conflict policies may not have the highest benefit-cost ratio, Dunne argues that they are crucial in ensuring successful development can occur. For that reason, these policies are already attracting considerable resources from the international donor community.

Dunne emphasizes that although he has examined many of the different ways that conflicts impose a cost on society, the true cost is still likely to be hugely underestimated. There are immeasurable quantities and legacy costs that are difficult to identify. The existence of drugs, criminal gangs, and violence in South American countries such as Colombia in the present day, for example, can be traced back to the ending of an armed conflict without true peace being achieved.

Too often, developed and stable nations have turned a blind eye to conflicts, done too little, too late. This analysis shows that, at the very least, from an economics perspective, there are sound reasons to change that approach. What’s your view? Are these investments that you think that policy-makers and philanthropists should prioritize? Have your say in the poll:

Remember: In each of the stories published to date, there’s a poll, and you can still go back and vote in all of the polls today. Each day, as well as publishing a new topic of research, I respond to your comments and update you on how readers are prioritizing pieces so far. See where readers’ priorities stand right now.

Tomorrow, we will wrap up our look at the Copenhagen Consensus 2012 research papers by examining education. Can we improve the quality of education that kids receive, or is quantity what matters?

In this series, Bjorn Lomborg explores the smartest investments to respond to global challenges—and readers get to have their say. See the earlier articles here. And read Bjorn’s responses to readers and find out which investments are currently at the top of Slate readers’ priority list. Be sure to vote in the poll at the bottom of each article.