Black Death Plague forced people to revolt. This let to collapse of feudalism.
Feudalism was the metaphorical "band aid" from after the Roman empire's collapse in 476 until the rennaisance.
The french
William the conqueror
The Crusades caused many nobles and knights to leave their land which caused feudalism to decline. Because of the decline in feudalism, many kings took the opprotunity to come to power and create a kingdom.
The loss of serfs on the manor.
Indirectly, the fall of Rome, and more directly, the threat of Viking attack. Viking raids during the Medieval period were common -- it WAS the Viking Age -- and what people do when they're under attack is run to the nearest fortified building. This building was either a church or the hall of a lord. Hence, in return for shelter and protection in case of emergencies, the lords asked for the loyalty and services of the peasants. Thus, feudalism.
Caused
The weight of the snow caused the roof to collapse. Her nervous disposition lead to a total collapse.
The middle ages- 1000-1500 AD.
Black Death caused people to loose faith. Thus it resulted in revolts against feudalism.
Are you talking about a economical collapse or about the 9/11 attacks ?