The Crusades were a series of Christian military expeditions which took place between the 11th and 13th centuries in an effort to reclaim the Holy Land from the Muslims. Since 638 when the Muslims took Jerusalem from the Byzantine Empire the Muslims posed a large threat to Europe. Over the centuries the Muslims took more land in North Africa, the eastern shores of the Mediterranean, and most of Spain. Then in the 11th century the Pope became powerful enough to mobilize an assault on the Muslims. Many power hungry leaders set out on a "Crusade" to throw the Muslims out of the area once controlled by the Byzantine Empire. These leaders were looking to gain land power and gold from this military conquest. Both sides were determined to keep the holy land under their control. .
This set the sage for much brutality and a very dark time. Through the next three centuries there were four major and several minor crusades which took 100's of thousands of lives and caused a catastrophic loss of property. Some of the darkest events of the crusades were the Paupers Crusade, the blood bath in Jerusalem, the battle of Hattin, the destruction of Constantinople and the Children's Crusades. Despite all these atrocities however some positive things did come out of the crusades. The Crusades marked the first time Western Europe was united with a common goal. It was the first time a great number of Western Europeans traveled carrying their culture and religion with them. The Christians learned to live in different cultures which they assimilated into their own while at the same time leaving their own imprint on those cultures (www.Encarta.com). This helped increase trade between these areas and Europe. The Crusades did represent a dark side of medieval behavior with some positive effects.
The First Crusade began when the Byzantine emperor Alesios's asked Pope Urban II, the Christian religious leader of Western Europe, for help to reclaim the former Byzantine territories in Asia Minor which had been taken by the Seljuk Turks.