21)
as a result of the black death (bubonic plague)
the aztec civilization was nearly destroyed.
the crusades failed to achieve their objective.
the decline of the feudal system was accelerated.
d
the mongols were able to take much of the middle east.

As a result of the Black Death, the decline of the feudal system was accelerated.

Explanation:

The Black Death is the name given by modern historians to a bubonic plague pandemic which raged in the Middle Ages, in the mid-1300s. This pandemic has affected Europe, Asia, North Africa and possibly sub-Saharan Africa.

It killed 30 to 50% of Europeans in five years (1347-1352), causing around 25 million victims. Its consequences on European civilization were severe and long, especially since this first wave is considered to be the explosive and devastating beginning of the second pandemic of plague which lasted, more sporadically, until the beginning of the 19th century.

This pandemic generated the fall of the European feudal regimes, both by the death of the feudal lords themselves, and by the death of many of their vassals, which generated a power vacuum due to the lack of protection that they could grant each other. Furthermore, this pandemic highlighted the need for centralized superior governments that could provide solutions to these borderline situations.

they were the direct result of some cultural difussion.