Lol, I just finished this in the course in school! The crusades change Europe's History, for positive and negative reasons. For one negatively there were many large Massacres, and the deaths of many innocent Jews. The looting of Constantinople. Positively, the spread of religions and faith. The also the spread of new ideas and becomes more multicultural.
Hope this helped. There are many more negative and positive reasons why the crusades changed Europe's history.