The bubonic plague killed more people than any other

The argument

The bubonic plague, or Black Death, emerged in the 14th century. Originally spreading to humans from rats, the pandemic killed roughly 200 million people, about half of Europe's population. It took over 200 years for the continent's population to recover. This places Black Death as the deadliest pandemic in history by a significant margin - second place belonging to smallpox, which killed 50 million people. The disease was also terrifyingly contagious and deadly. Simply touching a sick person was said to be enough to infect someone else, and people who were healthy in the evening could be dead by the morning. The Black Death was unprecedented in its deadliness, in a way that certainly has not been seen since.

Premises

Counter-arguments

The figures do not hold together. Europe's fourteenth-century population is generally estimated at well under 100 million, so a toll that was 'about half of Europe's population' cannot also be 200 million; the two numbers in the same sentence are incompatible. Mainstream estimates put European deaths from the Black Death in the tens of millions, with wider and much more speculative ranges when Asia and the Middle East are included. The comparison that follows is also mistaken. Smallpox is not a 50-million-death pandemic: conventional estimates credit it with hundreds of millions of deaths in the twentieth century alone, before counting the centuries preceding it or the catastrophic mortality it caused in the Americas after 1492. On absolute deaths, then, the claimed margin runs the other way. The contagion detail is inaccurate too. Bubonic plague is transmitted by fleas rather than by touch; person-to-person spread by droplet occurs in the pneumonic form, which is a different presentation of the same bacterium. 'Simply touching a sick person' describes fourteenth-century belief, not the mechanism. Underneath all of this sits the question's real difficulty: 'worst' is metric-dependent, and the argument silently picks one metric. On proportion of a population killed, the Black Death has a strong case in Europe — as does the Plague of Justinian, and as do the post-contact epidemics in the Americas. On absolute deaths, smallpox leads. On duration and continuing burden, HIV/AIDS and tuberculosis compete. Each rival position in this debate is defending a different measure, and asserting one of them is not an argument for it.

Rejecting the premises

[Rejecting P1] The figures are internally inconsistent: Europe's fourteenth-century population is estimated at well under 100 million, so half of it cannot be 200 million. Mainstream estimates place European deaths in the tens of millions. [Rejecting P2] Smallpox is credited with far more than 50 million deaths — conventional estimates run to hundreds of millions in the twentieth century alone — so the claimed margin over the next-deadliest pandemic does not hold. The contagion description is also wrong: bubonic plague spreads through flea bites, with person-to-person transmission confined to the pneumonic form.