In the Medieval ages there was a social pyramid called fuedalism. The Pope was the ruler over all, then it was the king,then the lords and nobles, the the knights, then the peasants/serfs.
The peasants would produce all of the food for the whole manor. The only thing they would get in return would be land and protection.
One of the Popes realized that the Muslim religion was gaining power and was afraid of what that would do to Christianity. So he declared war upon Jerusalem.
Then the Black Plague happened, which made the whole society crumble. The peasant would die due to the very unsanitary condition, that caused the feudalism structure to fall apart. Sense the peasants had given everyone their food, when they died off, nobody would get food. The peasants would make the upper first class people pay for them to work, because of the fact that they could die if they touch anything that the infected people had touched.
Many symptoms of having the disease is black finger tips, blood boils, vomiting blood, bad diarrhea, and also fever. The plague killed 1/3 of the population of Europe, it had come from Asia on a boat, from there the rats on the boat had fleas on them, which ended up biting the people.
The Church had started to loose power after the plague, because the church promised that the plague was because of their sins, when in reality, it wasn't at all. The church told people to buy indulgences to make the plague go away, but once again it didn't work. The church kept people from reading the bible, because in the bible it doesn't say anything about buying indulgences.