Why did the Crusades have such a significant impact on our modern world?

The lasting effects of the Crusades are really twofold. First, the Crusades facilitated direct contact between Europeans and the Middle East, which was in turn connected by a complex series of trade networks with the rest of Asia and Africa. This helped to spark increased demand for Asian goods, especially spices, and gold from Africa. A desire to maximize profit from these trades led European merchants and monarchs to promote voyages of exploration. The Crusades also exposed European scholars to the learning of the Arab world, a major intellectual development. 

Another major effect of the Crusades has been quite tragic. The Crusades were unfortunately a touchstone in relations between the western world and the Middle East. The word "crusader" remains an epithet in the Muslim world, one which has become relevant over the years following World War II, as the Ottoman Empire collapsed and western powers became increasingly involved in the region. There is little doubt that memory of the Crusades serves as a frame of reference for western involvement in the region.