The sociologist Charles Tilly (1929-2008) famously argued that “war makes the state”—that borders and bureaucracies were forged by necessity in military conflict. Plague had similar effects, requiring “military commitment, administration, finance and all the rest of it,” Mr. Snowden says. In addition to a navy to enforce quarantines, “you needed to have a police power,” a monopoly on force over a wide area. Sometimes “watchmen were stationed outside the homes of people who had the plague, and no one was allowed in or out.”

Yet while the plague saw power move up from villages and city-states to national capitals, the coronavirus is encouraging a devolution of authority from supranational units to the nation-state. This is most obvious in the European Union, where member states are setting their own responses. Open borders within the EU have been closed, and some countries have restricted export of medical supplies. The virus has heightened tensions between the U.S. and China, as Beijing tries to protect its image and Americans worry about access to medical supply chains.

The coronavirus is threatening “the economic and political sinews of globalization, and causing them to unravel to a certain degree,” Mr. Snowden says. He notes that “coronavirus is emphatically a disease of globalization.” The virus is striking hardest in cities that are “densely populated and linked by rapid air travel, by movements of tourists, of refugees, all kinds of businesspeople, all kinds of interlocking networks.”