At first, the Crusades were called for by the Christians to rescue the Christian shrines in the Holy Land from the Muslims. Muslim religion began in the seventh century in the area of present day Saudi Arabia. It spread throughout the Near East into the Mediterranean. Countries that once were Christian fell by the sword and became Muslim. The Eastern section of the Roman Empire (the Byzantine Empire based in Constantinople) was threatened by the invading Muslim or Ottoman Empire. Eventually, Constantinople did fall and became Istanbul.
At first, the Muslims of Palestine were peaceful toward Christians, who made pilgrimages to the various shrines dedicated to different aspects of our Lord’s life. The Muslims in power saw it as economic gain for everyone, and therefore Christians were tolerated. This was not to last. A fierce fighting tribe, the Seljuk Turks, invaded Palestine. As devout Muslims, they could not tolerate Christians in their territory. Reports of churches and shrines being burnt, Christians being murdered, and all sorts of persecution were brought back to the Christian West. Appeals from the Christian Byzantine Emperor in Constantinople, Pope Urban II, and the king of France, along with the Council of Clermont, called all Christians to take up arms and capture Jerusalem from the infidels. The rewards for their sacrifice would be spiritual blessings from God.
There would be eight major Crusades in all. The first was considered the most successful. It united royalty, nobility, clergy, and common folk. It accomplished what it set out to do: liberate Jerusalem and rescue Christian shrines in Palestine. Later, Christian city-states came into existence, and pilgrims once again could travel to the area. Constantinople, which stands at the door of the Muslim empire, was spared. However, this was short-lived. By 1270, many of the Crusades’ gains were lost, and Jerusalem once again came under Muslim control.
As a military campaign the Crusades were considered a failure, but they were a success in other areas. First, they united the people for a spiritual cause—to save the Holy Land Shrines. Second, they introduced the West to the finer things of the East, such as silks and spices. Third, the ancient writings of Aristotle were rediscovered, translated, and sparked a development in philosophy in the West. Finally, Christian communities, such as Maronites in Lebanon, became reconnected to the papacy.