The Crusades of the late eleventh to the thirteenth century had a substantial effect not only on Western Europe but also on the Byzantine Empire and the Middle East, as well as the relations between the three. The impact of the Crusades was felt even further afield if we count...
The Crusades of the late eleventh to the thirteenth century had a substantial effect not only on Western Europe but also on the Byzantine Empire and the Middle East, as well as the relations between the three. The impact of the Crusades was felt even further afield if we count among them, as many historians do, the attacks of the Teutonic Knights of the Livonian Order on Russian principalities of Pskov and Novgorod. In any case, the Crusades were an expansive phenomenon, and their effects were far-reaching and long-lasting. The brief comments below might suggest productive avenues to pursue to delve deeper into some of those effects.
The Crusades provided some benefits for Western Europe: they led to the development of the iron and shipping industries, the papacy grew in power and prestige after having spearheaded the wars and gained new adherents, the autonomy of women grew since men were away at war, and Europeans borrowed knowledge and skills from the societies they encountered in their campaigns.
While Europe benefited in some ways, the Crusades also brought problems. The slaughter of civilians created an image problem for Western Christians (Catholics) in the East, not only among the Muslim population but also local Christian and Jewish populations. During the First Crusade, the Western forces slaughtered Jews wholesale once they reached Jerusalem.
The Crusades also deepened the rift between the papacy and the Orthodox Christian world. If the first three crusades were marked by misunderstandings and tensions between the Western and Byzantine rulers, the brutal sack of Constantinople during the Fourth Crusade, according to the judgment of some historians, made the Great Schism of 1054 irreversible and permanent. Catholics, the Byzantines concluded, were certainly no brothers of the Orthodox.
Amin Maalouf, in his book The Crusades Through Arab Eyes, claims that the Crusades exposed the weaknesses of the Arab world. By that time, the leaders were foreigners: Turks, Armenians, and Kurds. Arabs had lost control of their own destiny. Military losses and a trail of problems in the wake of the Crusades revealed the absence of stable institutions and the lack of unity within Islam. Whereas western openness and borrowing from the lands they invaded contributed the Renaissance in the West, the Arab world, viewing itself as having been victimized by outside brutality, closed itself off and began to stagnate.
Any of these topics can be productively explored. There are fairly abundant primary and secondary sources on the Crusades and their impact. See the link below to get started.