The End of War? Who Should Get the Credit?
Not convinced? Well, you will have to look at the Easterbrook piece, or the original study, which measures "war" in a variety of ways: number of violent conflicts, numbers of war-related deaths, risk of death from war as compared to other causes, global military spending. The upshot? All of these measurements have shown a steady decline in the last 15 years.
Assuming this study is accurate, the important question becomes: what is the cause? Easterbrook throws some love to the UN, writing that, in addition to peacekeeping,
Peacekeeping is just one way in which the United Nations has made a significant contribution to the decline of war. American commentators love to disparage the organization in that big cereal-box building on the East River, and, of course, the United Nations has manifold faults. Yet we should not lose track of the fact that the global security system envisioned by the U.N. charter appears to be taking effect. Great-power military tensions are at the lowest level in centuries; wealthy nations are increasingly pressured by international diplomacy not to encourage war by client states; and much of the world respects U.N. guidance. Related to this, the rise in "international engagement," or the involvement of the world community in local disputes, increasingly mitigates against war.
This is certainly possible. But Easterbrook's review of possible causes curiously overlooks one important alternative. The U.S. has been calling itself the world's only superpower for about, oh, 15 years. Some have already proclaims this period a potential Pax Americana or American Imperium. The reduction in great power military tensions might reflect better diplomacy or it could simply reflect the overwhelming supremacy of U.S. military forces.
It is likely that all of these factors, and more not discussed here, have led to the comparative reduction in wars over the past 15 years (assuming that is really happening). The important question going forward then, is to figure out how best to keep the trendline heading downward.

