I think that one of the biggest changes in Europe is the role, wealth and power of the Catholic Church. The people set off for the holy land in search of the blessings and benedictions of the Pope. At the same time the papacy was getting alot of land for very cheap or nothing at all. This gave the church the upper hand in the fight for power.
The other important change was the intellectual development of Europe. With the new ideas from the East that helped liberalize the European minds came a more secular environment. The return from the East with new foods, culture and ideas greatly influenced the learning in Europe and eventually resulted in the great intellectual outburst known as "the revival of learning" and the period of the "Renaissance".
Some other major changes were the social and political changes. The social changes were represented in the way people acted socially. Many stories of Knights and Chivalry garnished the already blooming intrest in poetry. As for the political changes in Europe they mainly revolved around the depreciation of the feudal system and furthermore to it's extinction. At the same time the many cities gained political advantages and independance at the expense of the crusading Barrens and Princes. The crusades gave the early German Christians time to acquire strength enough to push back the Mohammedan Invasion in the 15th century.
The economical impact on the feudal system in Europe was the main reason for many of the Kings and Knights to mortgage or sell their lands in order to raise money for the crusading expeditions. Also, the killing of thousands of Lords and Kings in the holy land lead to a prodigious amount of unowned estates and lands. These were either sold to the church for a fraction of the price or given to the papacy in the name of God.
The material development of Europe was mainly caused by the voyages of discovery to the East. The crusaders acquired great wealth from the products and goods that they brought back. This made many Western Europeans increase their demands for foreign products. This lead to the increase of trade, which lead to the creation of new trade cities, such as Venice, Pisa and Genoa. This also lead to the increase in ship architecture and ship building. Through the increased trade and crusades many new arts, technology and inventions that were previously unknown to Europe were introduced from Asia and the Middle East.
A reborn interest in the earth's many diverse cultures could have been a deciding factor in Columbus's decision to go to the Americas and Sir Mandeville's decision to explore the remote countries of Asia. Marco Polo was one of the best examples of the renewed geographical interest in Europe after the crusades.
In my opinion, the most important effect of the crusades on Eurpoe was the commerce. The crusades created a constant demand for trade, encouraged ship building, and brought many great ideas, foods and philosophies from the Middle East and Asia to the everyday people of Europe. The crusades opened up an entire new world of food, culture and sheer discovery to an old, dull, dark, damp English castle.
