The Black Death is the name given to a devastating epidemic that took place between the years of 1347 and 1351 (with many other occurences at other times). The plague was caused by the bacteria Yersinia pestis, and it was responsible for the death of 75 to 200 million peope in Eurasia. This also led to many cultural, social and political changes, particularly in the European context.
The Crusades were a series of religious wars encouraged by the Catholic Church during the Middle Ages. They were designed to recover the Holy Land in the eastern Mediterranean from Muslim rule. The Crusades allowed the Church to consolidate a unified image. It also contributed to western culture by giving rise to accounts of heroism, chivalry, piety and romance in philosophy and literature.
The Mongol invasions and conquests took place during the 13th century, giving rise to one of the greatest empires in history, as well as one of the most devastatings. By 1300, the empire controlled much of Eurasia. They also became established in many countries, such as the Yuan dynasty of China, the Timurid Empire of Persia and the Mughal Empire of India.