As in all major historic events, the results of the Crusades were varied, complex and open to discussion as to their true effect upon World History. That being said there are some very important historic trends that can be seen as stemming from the Crusades:
Kingdoms of Europe are the now the norm, the chance of a United Europe under the leadership of the Church or single powerful leader is gone. Much of the wealth taken from the looting of the cities of the Middle East and new trade will pay for the growth of the more powerful of these kingdoms.
Distrust, Dislike and Outright Hatred between Christian and Muslims is now common due to the acts of bloody massacre and intolerance, accomplished “in God’s Name,” by the warriors and leaders of each group towards their "Enemies of the True Faith."
The Europeans desire for lost and new knowledge and Eastern trade goods, especially spices, is multiplied throughout Europe by the Crusaders hundred year presence in the Middle East terminus of the Silk and Spice Roads. This will lead to ever more expeditions looking for faster, cheaper and more profitable trade routes to “India and China.” These trade routes will require save havens, “Colonies,” for the Europeans as they travel from the West to the East.
Europe is once again interested in the rest of the World, a concept that had lain dormant in the West since the fall of the Western Roman Empire. More effort to understand the World, map the World and own their fair share of the World will consume the minds and energies of generations of European leaders, explorers, merchants and warriors.
Europe will now step on to the road of World conquest, slow at first but increasing in effort and violence faster as the centuries roll on. This conquest will continue, eventually resulting in the massive colonial Empires of the 19th/20th centuries, causing political, social and economic problems that the World still faces in the 21st century.