Because it involved countries all over the world, there was new technology such as chemical warfare, tanks, planes, etc. and it was unrestricted warfare. The countries were attacking civilians as well. Also there were diseases.
So that there was not too much power in one branch so that it overpowered another branch.
Although the Crusades are popularly viewed as religiously inspired campaigns to recapture the Holy Land, students should recognize them as a result of the social and economic events in Europe between 1000 and 1200. Religious and secular leaders seeking to end the fighting among feudal lords seized upon the Crusades as a means of redirecting that aggression. Feudal knights who would not be inheriting their family properties eagerly enlisted in the Crusades as a way to win wealth or status. The idea of the pilgrimage was a powerful one, and the Crusades were basically armed pilgrimages to the Holy Land. The various Crusades ultimately failed. The sack of Constantinople was a fitting denouement to the whole concept. The interaction with the East brought to Europe not only Arabic translations of Greek texts, but also original Arabic and Iranian scientific and philosophical works.
A. The U.S. put a naval blockade around Cuba.
