In recent years, authors have claimed that many seemingly boring things have changed the world but a particularly strong case can be made for the potato and Charles C. Mann makes it.
The effects of this transformation were so striking that any general history of Europe without an entry in its index for S. tuberosum should be ignored. Hunger was a familiar presence in 17th- and 18th-century Europe. Cities were provisioned reasonably well in most years, their granaries carefully monitored, but country people teetered on a precipice. France, the historian Fernand Braudel once calculated, had 40 nationwide famines between 1500 and 1800, more than one per decade. This appalling figure is an underestimate, he wrote, “because it omits the hundreds and hundreds of local famines.” France was not exceptional; England had 17 national and big regional famines between 1523 and 1623. The continent simply could not reliably feed itself.
The potato changed all that. Every year, many farmers left fallow as much as half of their grain land, to rest the soil and fight weeds (which were plowed under in summer). Now smallholders could grow potatoes on the fallow land, controlling weeds by hoeing. Because potatoes were so productive, the effective result, in terms of calories, was to double Europe’s food supply.
Mann talks more about the potato in his excellent 1493: Uncovering the New World Columbus Created.