In the 50 years following the First Crusade, the Latin states in the East were consolidated, but there were also growing tensions and new challenges. Against this backdrop, the fall of the County of Edessa in December 1144 at the hands of Zengi, the atabeg of Aleppo and Mosul, was a catastrophic event. Founded in 1098 by the future King Baldwin of Boulogne, Edessa was the first Crusader state, as well as the northernmost, weakest, and least populated. It was constantly exposed to Muslim attacks, and news of its fall reached Europe at the beginning of 1145, and the fall was the catalyst for the Second Crusade. Furthermore, the Crusader states were also concerned about their relationship with the Byzantine Empire. Relations with the Empire were often tense. As early as 1105, Bohemond of Antioch travelled to the West in search of troops to fight the Muslims while concealing his intention to attack parts of the Byzantine Empire. He reportedly obtained papal acquiescence, though not an explicit bull.
Historically, writers have given little prominence to the Second Crusade because of its failure, and it is understandably overshadowed by the triumphant First Crusade and the more captivating Third Crusade. For a long time, historiography attributed a central role to Bernard of Clairvaux, sometimes portraying him as the sole architect of the enterprise due to the political difficulties experienced by Pope Eugene III in Rome. However, more recent studies have re-evaluated the Pope's role, emphasizing his commitment to planning and coordinating the crusade through a network of legates and advisors. Contrary to the portrayal of him as a naïve monk, Eugene III had a profound grasp of the dynamics of crusading and the boundaries of Christendom, which informed his bull and overall strategy. Another historiographical issue concerns the scope of the crusade itself:
