Borders mark off the sovereign territory of one people from another. They are a means — if they can be enforced and defended — for a sovereign state to protect its people from invaders and unwelcome immigrants and goods. They are a tool almost every nation has used to try to keep the coronavirus from gaining a foothold in its population, and try to keep it from spreading further.

The lyrics of the treacly John Lennon classic “Imagine” — recently performed by celebrities organized by actress Gal Gadot as a balm in this time of distress — have never been so absurdly inapt. If there were really no countries and the world were as one, we’d be even more vulnerable to whatever threat arises across the globe in a city in central China.

Of course, travel restrictions haven’t prevented the spread of the disease — there’s no such thing as an air-tight seal against the virus. But restrictions at least bought governments some additional time, and openness to foreign travel from China has been an accelerant on its spread. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, says the presence of Chinese tourists in Italy was a factor in the severity of the epidemic there.