When the Black Death struck Europe in 1347, it destroyed a way of life that had taken centuries to develop. European society had arisen from a much earlier catastrophe—the fall of the Roman Empire in the fifth century.

At its zenith, Rome provided stability for millions of peoples from Italy to England and from North Africa to the Mideast. Eventually, though, government corruption, massive economic problems, moral decay, and repeated invasions of barbarian armies brought the empire tumbling down. Law and order soon vanished. Literacy and public education declined. Roads and highways fell into disrepair. Business transactions withered, and the use of money faded. Crime shot up. With the breakdown of civilization, people everywhere abandoned the once prosperous Roman cities and fled to the rural countryside. Here, they hoped to evade dangerous outlaws and seek their livelihood from the land.

Europeans...