The Third Plague Pandemic

The same bacterium that emptied Justinian's empire and killed a third of medieval Europe came out of southwestern China, reached Hong Kong in 1894, and travelled the world's steamship routes — killing over twelve million people, most of them in India. But this time two researchers isolated the bacillus within weeks of arriving, and a few years later others worked out that fleas on rats were carrying it. The killer that had emptied cities since antiquity was finally identified, named, and made survivable. Understanding it took 1,500 years; treating it took a few decades more.