After the Roman Emperor Constantine's conversion to Christianity, he and his mother "Helena" began to oversee the recovery of several important Christian sites; which included the newly discovered tomb of Christ. These discoveries led to a creation of a "Holy land", within the city of Jerusalem, which add a new dimension to the Christian experience. Christians were not only able to read about these sites, but by traveling the 3000 miles to Jerusalem could see and touch these holy relics. As part of the development in the "Holy Land" Constantine built the "Church of the Holy Sepulcher", which is known as the spot where Jesus was crucified and then later buried. Safety was guaranteed to the pilgrimages that traveled to Jerusalem in search of the ancient sites of Christianity until; "Muslims" took control and restricted travel to the city. However, the church of the Holy Sepulcher, continued to function as a Christian church until Muslim ruler "Hakim" destroyed the church. To European Christians the city was important to their beliefs and the destruction of the church forced the European nations to prepare for an aggressive Muslim invasion.
Islamic expansion in Europe had already taken place as Muslims invaded through Spain. Charles Martel saved Europe by defeating the Muslim forces at Poitiers, France in 732, forcing the Muslims to retreat back into Spain, until Spanish Christians attempted to reconquer their lands in the 11th century. This aggressive invasion into Europe only foreshadowed later attacks by the Islamic armies. The Byzantine Empire represented Europe's last defense against the Muslims invasion force. In 1071 Muslim armies attacked and defeated the Byzantines at Manzikert, this invasion began a long series of skirmishes and battles between the two nations, and after several setbacks and territorial losses to the Muslim nation Byzantine Empire lost its hold over Asia Minor. In 1081 Alexius I Comnenus became ruler of the Byzantine Empire, and held off several Islamic attacks allowing Byzantine to reestablish a stronghold in Asia once again. In 1094 Byzantine Emperor Alexius, requested military help from the Catholic Church in fighting the Muslim invasion.
As tales of attacks and atrocities on pilgrims returning from the "Holy Land" spread throughout Europe, along with stories of desecration to Christian Holy relics in Jerusalem, caused a great outrage among European Christians. Pope Urban II called for a pilgrimage to free the "Holy Land" from oppression by the Islamic religion and rule. The Pope also hoped to use the Crusades to unite the European people in a common cause as well. With the fall of Rome the European continent fell into hundreds of kingdoms, which were constantly fighting among themselves; also after the Viking threat had ceased there was a new social class that had developed after the subsequent wars and attacks by foreign threats. This class of warriors or "knights" lacked any useful activities other than fighting. And the Pope wanted to reduce the number of knights in Europe in order to reduce the fighting between European nations so that European monarchs, who were loyal to the Catholic Church would be able to consolidate their control and power more easily. These acts would help Pope Urban II reconsolidate the Church's power and reform the Catholic Church in Europe.
In-order to recruit the nobles and knight the Pope declared a decree that those who died in the campaign to free Jerusalem would receive liberation of their sins. The Pope had targeted French nobles and knights and wanted a well trained army that was controlled by the Church; however others, mostly peasants, were attracted to support the cause. With a recovering European economy and a new spirit of adventure, Europeans no longer waited for an attack from outside forces, they eagerly sent their armies to expand its territory and power in other nations. The kingdoms needed more land to cultivate, as they were not raising enough crops to feed its people properly, and in 1905 a famine due to food shortages broke out in Northern France. Also the middle class or "peasants" were aware of the profits that could be made through trade with Eastern nations, and many joined the crusade in search of wealth and a better life, by trading directly with the Muslims. Others wanted to actively participate in the religious reform sweeping through Europe, and do something in honor of their God.
Peter the Hermit lead the first Crusade in 1096, "The Peasants Crusade", which began in France and passed through Germany. While in Germany the makeshift army began plundering and destroying Jewish communities. Due to the preaching to raise men and efforts for the Christian Crusade many viewed the Jews as much of an enemy as the Muslims, since the Jews were held responsible for the crucifixion of Jesus Christ. Many of the peasants who had joined the crusade had to purchase weaponry and equipment for the Crusade, and since most were already poor or bankrupt they borrowed the money from Jewish communities to pay for their expenses. Many of these peasant Crusaders rationalized killing of the Jews both by their need for money and as an extension of their Christian fight against non-Christian believers. As many of the Crusaders were not provided for along their trip, in order to restock their supplies, the Christian peasant Crusaders began to plunder the food and property of the Jewish communities, while forcing the Jews to convert to Christianity. The Catholic Church condemned the persecution of the Jews and attempted to prevent the forced conversions in many areas, however their attempts were unable to stop the horrific acts enforced on the Jewish people. In part the First Crusade foreshadowed the organized violence against European Jewish culture.
Many followers of "Peter the Hermit" failed to make the final destination of joining the Byzantine army. And as they arrived the Byzantines were appalled with the army of peasants, which included women and children, as the Byzantines had hoped for a well trained and disciplined military fighting force. Alexius I Comnenus was especially displeased with the mob as he was now forced by the Catholic Church to feed and provide for the peasant Crusaders. Peter's army was quickly shipped across the straights and into Asia Minor to join the fighting forces, where they were made no progress against the Turkish forces and were eventually massacred.
The warrior class or "Knightly" Crusade was organized in the summer of 1096. Pope Urban II appointed "Adhemar, Biship of Le Puy" as leader of the Knightly Crusade, as the armies arrived in Constantinople, Alexius I Comnenus quartered the troops outside the city, quickly resupplying them before leading them into Asia Minor. Although the armies were warned to proceed around the coast of the peninsula, they decided to take the shortest route and marched through the middle. They quickly captured the city of Nicaea where the Byzantium Emperor Alexius I Comnenus claimed the areas for Byzantium. The Byzantium Emperor was willing to allow the European Crusaders to develop principalities for themselves in captured Turkish controlled land if the new states agreed to be under his control as Emperor. In doing this he required that each European lord to an "oath of Liege" upon their arrival to join the Crusade. After conquering Nicaea, the armies continued their march through Asia Minor, defeating the Muslims at Dorylaeum and Edessa; where Baldwin of Bouillon became count of the first crusader state. The armies then moved on to a seven month siege of Antioch. After the Crusaders defeated the Muslim army at Antioch it became the second state held by the army of the Crusaders. The Crusaders arrived at Jerusalem in the summer of 1099 and after a short month long siege and the massacre of Muslims and Jews the Christian Crusaders took control of the city and essentially freed the "Holy Land" from control of the infidels who had destroyed most of the sacred Christian artifacts.
The effects of the Crusades were an important factor in the progress of civilization. The Crusades influenced the power of the Catholic Church, social changes and prompted the Voyages of discovery. The Crusades contributed to the power of the Catholic Church by placing the armies of the European nations within their control, the Church consolidated its power in Europe by organizing and controlling the Crusades and freeing the "Holy Land" from Muslim control and eliminating the fighting among European rulers, they forced the nations of Europe to look to them as leaders. Commerce was also strongly affected by the Crusades as the demand for transportation of supplies and men, to reinforce the armies of the Crusaders, encouraged ship-building which lead to an increase in naval vessels for European nations. The Crusades also helped to open up the market for trade goods in Europe, as many Oriental products such as silks, precious stones and spices found their way into European consumer markets. And the incentive to find a shorter route to the supplying nations of these sought after goods, helped to start the many voyages of discovery such as "Marco Polo" and later the voyages of Columbus.