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The bubonic plague, which killed around 1/5 of the world’s population in the 14th century, is still around today -- but it now claims only a few thousand lives each year. How did that number shrink so drastically? Sharon N. DeWitte investigates the causes and effects of the black death and explains how knowing this information can help us prepare for any future outbreaks of the disease.

Lesson by Sharon N. DeWitte, animation by Steff Lee.