Which historical event was most responsible for the spread of the Bubonic Plague in Europe?
increased use of the feudal system in Asia
increased trade along the Silk Road
the unification of the Holy Roman Empire
the development of the caste system in india

increased trade along the Silk Road

Explanation:

Great Bubonic Plague was brought in Europe in the middle of 14th Century by traders from Genoa. Of course, as we know after the Crusades the trade between Europe and Asia was increased. That is why traders from Venetian Republic, Genoa and other Italian city states were trading a lot with them. Still, this brought many dangers, because as we can see one of the things that was brought from there was the plague.

1. it was caused by feudalism

2. charlemagne used christianity as a major cornerstone for his rule. cloisters were built all over the empire to act as centers for the (re)population of the vast european wilderness.

3. the europeans feared the next raid every time chetak

i'm not so sure about #6. but i hope i you with the first 3.