The second Crusade much like the first, was a responce the a Muslim invasion of the city Edessa. The Muslims presented a greater threat now than before simply because the early Muslims of the first Crusade were not united but isolated weaker Muslim groups. The leader of the attack on Edessa and reunification of the Muslims was Imad ad-Din Zangi (1084-1146), ruler of Mosul and Aleppo. The papacy proclaimed the Second Crusade in 1145. King of France, Louis VII, and Holy Roman Emperor, Conrad III were among the people who chose to march against the Muslims. Conrads German army left in May 1147, the French followed about a month later. In Anatolia the Germans fell into an ambush, many didn't survive. The French suffered the same fate ,however, at least half of the army made it. After consulting with King Baldwin III of Jerusalem, the Crusaders attacked Damascus in July. They couldn't take the city and shorlty after the French king took what was left of his men and returned home.
The success of the Christians in the First Crusade had been largely due to the disunion among their enemies. But the Muslims learned in time the value of united action, and in 1144 A.D. they succeeded in capturing Edessa, one of the principal Christian outposts in the East. The fall of the city of Edessa, followed by the loss of the entire county of Edessa, aroused western Europe to the danger which threatened the Latin Kingdom of Jerusalem and led to another crusading enterprise. In the interval between the Second and the Third Crusade the two famed religious military orders, known as the Hospitallers and the Templars were formed. A little later during the Third Crusade still another fraternity, known as the Teutonic Knights was established. The objects of all the orders were the care of the sick and wounded crusaders, the entertainment of Christian pilgrims, the guarding of the holy places, and ceaseless battling for the Cross. These fraternities soon acquired a military fame that was spread throughout the Christian world. They were joined by many of the most illustrious knights of the West and through the gifts of the pious acquired great wealth and became possessed of numerous estates and castles in Europe as well as in Asia. The second crusade helped to crystalize Muslim feeling and was of special importance in the long range relations between East and West in the Middle Ages.
In 1147–49, the Second Crusade, championed by the abbot Bernard of Clairvaux, attempted to take Damascus in Syria. The campaign was a dismal failure because the Muslims had regrouped. Led by Salah al-Din (Saladin), Muslim forces advanced across Syria and finally retook Jerusalem in October 1187. By the end of the Third Crusade (1189–92), however, Crusader forces had gained Cyprus and the city of Acre. With each crusade, relations between the Byzantines and the Western forces became more estranged.
The Second Crusade, though begun under the most favorable auspices, had an unhappy ending. Of the great host that set out from Europe, only a few thousands escaped annihilation in Asia Minor at the hands of the Turks. Louis and Conrad, with the remnants of their armies, made a joint attack on Damascus, but had to raise the siege after a few days. This closed the crusade. As a chronicler of the expedition remarked "having practically accomplished nothing, the inglorious ones returned home." The strength of both the French and the German division of the expedition was wasted in Asia Minor, and the crusade accomplished nothing.
Even more important, perhaps, was the deterioration of relationships between Byzantium and the Crusaders and between the princes of the West and the rulers of the Latin states in the East. Most important of all, in the final analysis, was the effect of the Second Crusade upon the Muslims. The failure of the Crusade to achieve any victories whatever in the East emboldened Muslim military leaders, destroyed the myth of Western prowess in arms, and was to be responsible, at least in part, for causing the Muslim states of the East to draw closer together, to unite for further attacks upon the Latin states .