Two major effects of the Crusades were that the kings' authority increased and the Europeans learned about new things from the Muslims they encountered. During the Crusades, the kings increased taxes to fund the cause. Many peasants also left their land to fight, and when they died, the land went to the king. With large amounts of money and land coming in, the kings gained power.
The impact the Muslims had on the Europeans was huge in the areas of advancement and trade. The Europeans learned more about sailing and building ships, as well as the magnetic compass. They also gained a desire to trade with the rest of the world when they saw the silk, spices, art and literature of the Muslims. The growth of trade eventually led to the growth of the merchant class and the end of serfdom.
Another effect of the Crusades was that the Catholic Church grew in power and influence, especially politically. After the Crusades, there was an increased interest in learning, travel and the spreading of new ideas, which laid roots for the Renaissance. The Crusades also led to the Europeans' new knowledge of sea travel and increased interest in trade and other cultures, which opened up opportunities for explorers, such as Marco Polo and Columbus.