The Black Death plague of the 14th century was caused by bacteria found in rodents in Central Asia. It spread along trade routes, killing an estimated 20-40 million people in Europe, Asia, and Africa between 1347-1400. Symptoms included fever, chills, and swollen lymph nodes. Mongol armies besieging a Crimean city used infected corpses to spread the plague to Europe, where it devastated populations and economies and ended the feudal system due to labor shortages.