The Black Death or otherwise known as the bubonic plage was introduced into Europe by trade routes and then was carried by black rats infested with flies (doc 1). At the time they didn't have the medical experience to cure the plague or destroy it. Especially since the fall of Rome many of there teaching were lost with the civilization or the people did not have the intellect to understand them. Smallpox was brought over to South and Central America by Explorers (doc 4) .