Why was the black death caused

Yersinia pestis is a kind of disease that usually comes from flea's. The fleas come and spread the disease to animals. The reason the black death was so bad was because the fleas had no where to go. There wen't a lot of animals left so they had to turn to humans. They got infected and that is what made it so huge

It was caused by the spreading of a bacterial infection an passed around by rats in the 1600 in Europe this also lead to Colombus finding America