Michael Lind is the author of Land of Promise: An Economic History of the United States and co-founder of the New America Foundation.

In the aftermath of the Boston Marathon bombings, it is important to keep things in perspective, by emphasizing what the mass media tend to neglect — namely, the fact that the world has become much more peaceful in recent decades and is getting more peaceful all the time.

It does not diminish the horror of mass casualty attacks on civilians, in this and other countries, to point out that today’s terrorist incidents provide a counterpoint to a declining arc of political violence worldwide. Both violence among states and violence within states have diminished dramatically in the last few generations.

If we look at battle deaths in the last century, the spurts in the Cold War, associated with the Korean, Indochina and Soviet-Afghan wars, were dwarfed by the huge spikes of slaughter associated with the world wars. And with the end of the Cold War came a steep decline in political violence worldwide — mainly because the two sides no longer kept local conflicts going by arming and supplying opposing sides from Latin America to Africa to Asia and the Middle East.