what was the most responsible for the spread of the bubonic plague across Euasia

The bubonic plague, also known as the Black Death, was primarily spread across Eurasia by fleas that infested black rats. The rats often lived in close proximity to humans, especially in crowded cities and towns, providing an ideal environment for the transmission of the disease.

Factors that contributed to the spread of the plague include:

1. Trade and Commerce: The interconnectedness of trade routes during the 14th century facilitated the movement of infected rats and fleas across different regions, allowing the plague to spread rapidly. Major trade routes such as the Silk Road played a significant role in spreading the disease to new areas.

2. Urbanization and Crowded Living Conditions: Increasing urbanization led to higher population densities and unsanitary living conditions, which provided a hospitable environment for rats and their fleas. The close proximity and intermingling of individuals in urban centers facilitated the rapid transmission of the disease from person to person.

3. Lack of Knowledge and Hygiene: Limited understanding of disease transmission and inadequate hygiene practices further contributed to the spread of the plague. People lacked knowledge about the role of fleas in transmitting the disease, and poor sanitation and hygiene practices facilitated the proliferation of rat populations.

4. Movements of Armies, Soldiers, and Refugees: Wars and military campaigns during the 14th century involved large movements of armies, soldiers, and refugees, providing opportunities for the disease to be spread across different regions. Displaced populations often carried the infected rats with them, leading to new outbreaks in previously unaffected areas.

5. Lack of Medical Infrastructure: The lack of advanced medical knowledge and healthcare infrastructure in that era made it challenging to identify and control the disease effectively. Limited medical resources led to a higher mortality rate and increased the chances of the plague spreading unchecked.

Overall, the combination of factors such as trade networks, urbanization, poor hygiene, movements of populations, and limited medical knowledge and infrastructure were responsible for the rapid spread of the bubonic plague across Eurasia.