The document discusses the Black Death plague that hit Europe in the 1300s, caused by bacteria transmitted from black rats and fleas. It killed around 25 million people in Europe when the population was only 37 million, spreading from China through 11 locations from 1348 to 1388. The plague had devastating economic and social impacts as it decreased the population and labor force while increasing wages, and disproportionately killed children, old people, and the wealthy.