Economic historian Goodspeed discusses what triggers recessions and why war is the most prolific “serial killer” of economic expansions over the last 400 years. We would expect that higher, faster, longer economic expansions should be followed by deeper, faster, longer recessions. Expansions don’t die of old age; deeper, faster, longer recessions don’t follow higher, faster, longer expansions; recessions have become less frequent over time. But you say there’s one thing that’s been “a prolific serial killer of economic expansions” over the last 400 years: war. It’s especially puzzling since the U.S. notched two of its longest economic expansions ever in the last few decades, and expansions exert greater overall influence on an economy.