The Crusades lasted roughly 200 years. There were many casualties, and few successes. The period of war soured relations between Christians and Muslims, a feud that still exists to this day.
In spite of this, the Crusades did have a number of positive impacts on history. One example of this would be the end of feudalism. As knights were dying, so was Western Europe's feudal system.
Changes brought about by the Crusades, such as Europe's exposure to other nations and the introduction of a money economy in the West, contributed to the decline of feudalism.
Today's world would be a much different place if feudalism still existed in government. Democracy and capitalism, which have gained popularity throughout the world's nations, are very unlike the feudal system.