1. The Second Crusade was launched in response to the capture of Edessa by Zengi, the Seljuk ruler of Mosul, in 1144. The First Crusade had been launched in response to the Seljuk capture of Jerusalem in 1071.
2. The Second Crusade was led by two kings, Louis VII of France and Conrad III of Germany, while the First Crusade had been led by a variety of nobles and clergymen.
3. The Second Crusade was a much larger and better-organized expedition than the First Crusade. It is estimated that the Second Crusade involved around 100,000 men, while the First Crusade had involved around 30,000 men.
4. The Second Crusade was much less successful than the First Crusade. The crusaders failed to recapture Edessa and were defeated at the Battle of Hattin in 1187. Jerusalem fell to Saladin, the Ayyubid sultan of Egypt and Syria, in the same year.
5. The Second Crusade had a number of negative consequences, including the massacre of Jews in Europe, the rise of religious intolerance, and the weakening of the Byzantine Empire.