The Second Crusade (1147-1149) was a military campaign organised by the Pope and European nobles to recapture the city of Edessa in Mesopotamia which had fallen in 1144 to the Muslim Seljuk Turks. Despite an army of 60,000 and the presence of two western kings, the crusade was not successful in the Levant and caused further tension between the Byzantine Empire and the west. The Second Crusade also included significant campaigns in the Iberian peninsula and the Baltic against the Muslim Moors and pagan Europeans respectively. Both secondary campaigns were largely successful but the main objective, to free the Latin East from the threat of Muslim occupation, would remain unfulfilled, and so further crusades over the next two centuries would be called, all with only marginal successes.
This is a companion discussion topic for the original content at https://www.worldhistory.org/Second_Crusade/.