Answer:
Wars between rulers for conquering lands and crusades.
Step-by-step explanation:
The Middle ages were under wars that required the knights to fight for their king. Young men were eager to join as knight or foot soldiers against their enemy. Europe, during this period, was under a situation where they were attacked by Muslim rulers which led many Christian lands to convert into Muslim.
The crusade played a crucial role in bringing men together and raise arms to fight the war against the Muslim. It encourages kings, knights, and commoners in Europe to fight for Holy land in Jerusalem.