What were the causes of the fourteenth century bubonic plague pandemic?

Plague, the disease caused by the bacterium Yersinia pestis, was the cause; Y. pestis infection most commonly results in bubonic plague, but can cause septicaemic or pneumonic plagues. ... In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million in the 14th century.

Explanation:

the answer is title i subtitle b

the roman army grew in size and became dominant in the mediterranean region.