A European living in a country conquered by the Mongols would most likely have a perspective that highlights the negative aspects of the Mongol conquests, such as the violence and upheaval caused by their invasions. Therefore, the response which aligns with this perspective would be:
The Mongols were responsible for the murder of millions of people in their conquest of European countries.
This viewpoint reflects the fear and resentment that a European subject under Mongol control might have had, emphasizing the destruction and loss of life associated with the Mongolian expansion.