Were the Crusades justified?

Of all the periods of history, few are more complex than the Crusades. Historians are said to be still trying to sort it out. Depending on the writer, any number of reasons are given for the strong response to Pope Urban II’s appeal to help fellow Christians in the Holy Land and curb the spread of Islam: Many crusaders were drawn by the papal forgiveness of sins and to gain eternal favor, some were motivated by a sense of adventure and booty, others had reasons that often conflicted with their fellow crusaders. Their ranks were often rife with petty jealousies and sometimes Christians fought Christians, which was certainly the case in the capture of Constantinople. Strange alliances developed, where Jews fought alongside Muslims against Christians in Jerusalem.

The crusades went on for over 150 years and descriptions of the horrors of the crusades are often ghastly, where one French eye witness at the fall of Jerusalem said “the carnage lasted for a week.” Perhaps the most terrible development was the Children’s Crusade in which large numbers of young French and German boys were caught up in the religious fervor and volunteered to go to Palestine. Many of them who arrived in Marseilles were tricked by slavers, who instead of taking them to Palestine, sold them into slavery in Egypt.

From our vantage point of time, was there any justification for the crusades?