What do you mean by Crusades? …

Crusades were the holy wars that were fought between the Muslims and the Christians for taking control of the ancient holy sites. 

• It led to the decline of feudalism in Europe
• While fighting holy wars against the Turkish Muslims, the crusaders learnt the use of guns and gunpowder. This discovery greatly undermined the importance of feudal lords and armoured knights.
• It now became difficult for them to defy the authority of the king, leading to the decline of feudalism and the consolidation of the powers of the king. 
• When the Europeans went to Asia to fight crusades, they learned several new ideas from the Muslims. It also increased the desire for trade with other parts of the world. This lead to the rise of the merchant class and the end of serfdom.
• The crusaders in their fight with the Muslims came into contact with several manuscripts pertaining to the Roman and Greek culture. Thus, began the process of learning these cultures leading to the beginning of the Renaissance in Europe.
• As a result of the Crusades, direct trade contacts were opened between the East and West. Trade began to flourish and the European economy started to improve.
•  As traders, bankers and artisans began to pay taxes, the wealth and the power of the king improved.