Negative effects of the Crusades included the repeated defeats of the Christian armies, the slaughter of innocents and the looting of Constantinople. The destruction of Constantinople severed any hope of mending the East-West schism in Christianity, and this event left the Byzantine Empire vulnerable to the Ottoman Empire.
Massacres during the First Crusade occurred when Count Emicho led a campaign that resulted in the murder of innocent Jews throughout the Rhineland during the First Crusade of 1096. This resulted in strained relations between Jews and Christians. Christian armies also slaughtered men, women and children by the hundreds on their way to capture Jerusalem.
Christian armies suffered numerous defeats throughout the Crusades. For instance, the armies of King Louis VII of France and King Conrad III of Germany were defeated during the Second Crusade at the hands of Muslim armies in Damascus. The Crusaders that occupied Jerusalem were conquered by Muslim ruler Saladin, which prompted the Third Crusade.
The pillaging of Constantinople occurred during the Fourth Crusade. Pope Innocent III toppled Alex III of Byzantine in favor of his nephew, who would later become Alexius IV. Alexius' attempt to impose Roman authority over Byzantine was met with resistance, and he was subsequently killed. The Crusaders declared war on Constantinople, which resulted in the conquest and looting of the city. Churches were also pillaged, and many people were killed.