The 80th anniversary of the Wall Street crash of 1929 is now upon us. But this time of year brings the anniversary of a few other infamous financial panics, too: 2008 (September and October, roughly), 1987 (Black Monday, Oct. 19), 1907 (began in October) and 1873 (began in September).

Autumn seems to beget a disproportionate share of American financial crises. But why?

Once upon a time, there was a relatively clear-cut explanation for fall financial market problems: the crop cycle.

From “The First Tycoon: The Epic Life of Cornelius Vanderbilt”:

As described earlier, the creation of a national bank system formalized the centralization of the U.S. financial structure in the city of New York. With the restriction of gold to specialized uses (mostly in...