The Old View, held by grandfatherly conformist historians, was that the disease Europeans called the Plague, or the Bubonic Plague, or the Black Plague, was one disease throughout history. In this decidedly retrograde theory, people who lived a long time ago were trusted to identify diseases, and it was assumed that this knowledge was somehow preserved in the medical community from 1348 down to the discovery of the plague bacillus (Yersinia pestis) in 1894.
Various bold rebel iconoclasts popped up every so often to say that this couldn't be true. Not that they had any very good reason for thinking this, they just knew that whatever the grandfatherly conformists taught must be wrong. Therefore they published articles arguing that past plagues were really measles, or typhus, or a hundred other things.
But now we have the technology to extract DNA from ancient skeletons, and we have learned that when people die of a disease their bones and teeth are full of bacterial DNA from the disease that killed them. So we can check to see what plague victims died of. And lo and behold, the grandfatherly conformists were right: the Black Death was the plague was Yersinia pestis. Take that, bold rebel iconoclasts.
But what about the Great Plague of 541-542, the Plague of Justinian? (It wasn't his fault, he just happened to be emperor at the time.) There wasn't much evidence on this one either way, just a supposition by small-minded, conservative, Occam's Razor sort of people that since Eurasia knows of only one disease that could wipe out half the population of a country, Justinian's Plague was likely to be that disease, too. Exactly the sort of logic that enrages revisionist crusaders, who mocked this mercilessly. But now we have data on this pestilence, too. The latest result comes from an unusual Bavarian cemetery of about the right date, where as many as three skeletons had been dumped into a single grave. It has the look of a plague cemetery. Examination of the skeletons produced lots of of Yersinia pestis.
What do you say now, bold rebel iconoclasts? Will you admit that sometimes the Old Establishment view is right? Could it be that you are not smarter than everyone who came before you?