What effects did the Crusades have on the Islamic world and Byzantium?
The Crusades began in answer to an urgent request from Byzantine Emperor Alexius Comneus to Pope Urban II to rid the area of Muslim Turks. Most scholars agree that the Crusades slowed the advance of Islam, with the presence of Crusader states in the Near East forming a barrier between the Arabs and Turks, preventing the formation of a unified Islamic power. Because effort had to be diverted to defense, it slowed the pace of conquest.
A side effect of the Crusades was new knowledge of the East, with possibilities for trade. However, this also encouraged additional violence, conquest, and bloodshed as religious interests combined with secular and military enterprises. This includes the belief that the military conquest of Constantinople actually hastened the fall of the Byzantine Empire, as it was never able to regain its former strength. Also, with new knowledge of trade, economic trends shifted as well. Commercial trading shifted from Muslims to Italians in the Mediterranean, with a gradual shift to the Atlantic, and Spain and Portugal seeking new trade routes and opening the world up to additional exploration.
The Crusaders launched attacks against the Muslim world in attempts to “liberate” Jerusalem, which they considered to be their Holy Land. The Crusades were religious wars waged with the approval of Christian leaders in Europe against the Muslims and Jews in the Middle East.
The Crusades had negative impacts on trade in the Middle East, which at the time played a key role in the global trade of products such as silk and spices. Sustained attacks by the Crusaders forced the Muslims and Jews to fortify their cities and retaliate against Christian aggression fronted by Europe. Some territory was lost by both the Muslims and Jews, but most of it was recovered years later.
Constantinople was attacked by crusaders during the fourth crusade, while it was still under Christian control. The different Christian factions failed in presenting a unified front. Schisms within the Christian fraternity provided an opportunity for Muslims to reclaim the captured territory.