Edessa was the first of the Crusader states to have been founded during the First Crusade (1095–1099), and was the first to fall. The Second Crusade was announced by Pope Eugene III, and was the first of the crusades to be led by European kings, namely Louis VII of France and Conrad III of Germany, with help from a number of other important European nobles. The armies of the two kings marched separately across Europe and were somewhat hindered by Byzantine emperor Manuel I Comnenus; after crossing Byzantine territory into Anatolia, both armies were separately defeated by the Seljuk Turks. Louis and Conrad and the remnants of their armies reached Jerusalem and, in 1148, participated in an ill-advised attack on Damascus. The crusade in the east was a failure for the crusaders and a great victory for the Muslims. It would ultimately lead to the fall of Jerusalem and the Third Crusade at the end of the 12th century.
The only success came outside of the Mediterranean, where Flemish, Frisian, Norman, English, Scottish, and some German crusaders, on the way by ship to the Holy Land, fortuitously stopped and helped the Portuguese in the capture of Lisbon in 1147.
In late 1144, Joscelin II allied with the Ortoqids and marched out of Edessa with almost his entire army to support the Ortoqid Kara Aslan against Aleppo. Zengi, already seeking to take advantage of Fulk's death in 1143, hurried north to besiege Edessa, which fell to him after a month on 24 December 1144. Manasses of Hierges, Philip of Milly and others were sent from Jerusalem to assist, but arrived too late. Joscelin II continued to rule the remnants of the county from Turbessel, but little by little the rest of the territory was captured or sold to the Byzantines. Zengi himself was praised throughout Islam as "defender of the faith" and al-Malik al-Mansur, "the victorious king". He did not pursue an attack on the remaining territory of Edessa, or the Principality of Antioch, as was feared. Events in Mosul compelled him to return home, and he once again set his sights on Damascus. However, he was assassinated by a slave in 1146 and was succeeded in Aleppo by his son Nur ad-Din.
For all his overmastering zeal, Bernard was by nature neither a bigot nor a persecutor. As in the First Crusade, the preaching inadvertently led to attacks on Jews; a fanatical French monk named Rudolf was apparently inspiring massacres of Jews in the Rhineland, Cologne, Mainz, Worms, and Speyer, with Rudolf claiming Jews were not contributing financially to the rescue of the Holy Land. Bernard, the Archbishop of Cologne and the Archbishop of Mainz were vehemently opposed to these attacks, and so Bernard traveled from Flanders to Germany to deal with the problem and quiet the mobs. Bernard then found Rudolf in Mainz and was able to silence him, returning him to his monastery.
Upset by German participation in the crusade, the Obotrites preemptively invaded Wagria in June 1147, leading to the march of the crusaders in late summer 1147. After expelling the Obodrites from Christian territory, the crusaders targeted the Obodrite fort at Dobin and the Liutizian fort at Demmin. The forces attacking Dobin included those of the Danes Canute V and Sweyn III, Archbishop Adalbert II of Bremen, and Duke Henry the Lion of Saxony. When some crusaders advocated ravaging the countryside, others objected by asking, "Is not the land we are devastating our land, and the people we are fighting our people? The Saxon army under Henry the Lion withdrew after the pagan chief, Niklot, agreed to have Dobin's garrison undergo baptism. After an unsuccessful siege of Demmin, a contingent of crusaders was diverted by the margraves to attack Pomerania instead. They reached the already Christian city Stettin, whereupon the crusaders dispersed after meeting with Bishop Albert of Pomerania and Prince Ratibor I of Pomerania. According to Bernard of Clairvaux, the goal of the crusade was to battle the pagan Slavs "until such a time as, by God's help, they shall either be converted or deleted". However, the crusade failed to achieve the conversion of most of the Wends. The Saxons achieved largely token conversions at Dobin, as the Slavs resorted to their pagan beliefs once the Christian armies dispersed. Albert of Pomerania explained, "If they had come to strengthen the Christian faith ... they should do so be preaching, not by arms".
By the end of the crusade, the countryside of Mecklenburg and Pomerania was plundered and depopulated with much bloodshed, especially by the troops of Henry the Lion. This was to help bring about more Christian victories in the future decades. The Slavic inhabitants also lost much of their methods of production, limiting their resistance in the future.
In the spring of 1147, the Pope authorized the expansion of the crusade into the Iberian peninsula, in the context of the Reconquista. He also authorized Alfonso VII of León to equate his campaigns against the Moors with the rest of the Second Crusade. In May 1147, the first contingents of crusaders left from Dartmouth in England for the Holy Land. Bad weather forced the ships to stop on the Portuguese coast, at the northern city of Porto on 16 June 1147. There they were convinced to meet with King Afonso I of Portugal.
The crusaders agreed to help the King attack Lisbon, with a solemn agreement that offered to them the pillage of the city's goods and the ransom money for expected prisoners. The Siege of Lisbon lasted from 1 July to 25 October 1147 when, after four months, the Moorish rulers agreed to surrender, primarily due to hunger within the city. Most of the crusaders settled in the newly captured city, but some of them set sail and continued to the Holy Land. Some of them, who had departed earlier, helped capture Santarém earlier in the same year. Later they also helped to conquer Sintra, Almada, Palmela and Setúbal, and were allowed to stay in the conquered lands, where they had offspring.
Elsewhere on the Iberian Peninsula at almost at the same time, Alfonso VII of León, Ramon Berenguer IV, Count of Barcelona, and others led a mixed army of Catalan and French crusaders against the rich port city of Almería. With support from a Genoese-Pisan navy, the city was occupied in October 1147. Ramon Berenger then invaded the lands of the Almoravid taifa kingdom of Valencia and Murcia. In December 1148, he captured Tortosa after a five-month siege again with the help of French and Genoese crusaders. The next year, Fraga, Lleida and Mequinenza in the confluence of the Segre and Ebro rivers fell to his army.
In battle, the Turks used their typical tactic of pretending to retreat, and then returning to attack the small force of German cavalry which had separated from the main army to chase them. Conrad began a slow retreat back to Constantinople, and his army was harassed daily by the Turks, who attacked stragglers and defeated the rearguard. Even Conrad was wounded in a skirmish with them. The other division, led by the King's half-brother, Bishop Otto of Freising, had marched south to the Mediterranean coast and was similarly defeated early in 1148.
Since the original negotiations between Louis and Manuel, Manuel had broken off his military campaign against the Sultanate of Rüm, signing a truce with his enemy Sultan Mesud I. This was done so that Manuel would be free to concentrate on defending his empire from the Crusaders, who had gained a reputation for theft and treachery since the First Crusade and were widely suspected of harbouring sinister designs on Constantinople. Nevertheless, Manuel's relations with the French army were somewhat better than with the Germans, and Louis was entertained lavishly in Constantinople. Some of the French were outraged by Manuel's truce with the Seljuks and called for an alliance with Roger II and an attack on Constantinople, but they were restrained by Louis.
When the armies from Savoy, Auvergne, and Montferrat joined Louis in Constantinople, having taken the land route through Italy and crossing from Brindisi to Durazzo, the entire army was shipped across the Bosporus to Asia Minor. The Greeks were encouraged by rumours that the Germans had captured Iconium, but Manuel refused to give Louis any Byzantine troops. Byzantium had just been invaded by Roger II of Sicily, and all of Manuel's army was needed in the Balkans. Both the Germans and French therefore entered Asia without any Byzantine assistance, unlike the armies of the First Crusade. In the tradition set by his grandfather Alexios I, Manuel also had the French swear to return to the Empire any territory they captured. The French met the remnants of Conrad's army at Nicaea, and Conrad joined Louis' force. They followed Otto of Freising's route, moving closer to the Mediterranean coast, and they arrived at Ephesus in December, where they learned that the Turks were preparing to attack them. Manuel also sent ambassadors complaining about the pillaging and plundering that Louis had done along the way, and there was no guarantee that the Byzantines would assist them against the Turks. Meanwhile Conrad fell sick and returned to Constantinople, where Manuel attended to him personally, and Louis, paying no attention to the warnings of a Turkish attack, marched out from Ephesus with the French and German survivors. The Turks were indeed waiting to attack, but in a small battle outside Ephesus, the French were victorious.
They reached Laodicea early in January 1148, around the same time Otto of Freising’s army had been destroyed in the same area. Resuming the march, the vanguard under Amadeus of Savoy became separated from the rest of the army, and Louis’ troops were routed by the Turks. Louis himself, according to Odo of Deuil, climbed a rock and was ignored by the Turks, who did not recognize him. The Turks did not bother to attack further and the French marched on to Adalia, continually harassed from afar by the Turks, who had also burned the land to prevent the French from replenishing their food, both for themselves and their horses. Louis no longer wanted to continue by land, and it was decided to gather a fleet at Adalia and sail for Antioch. After being delayed for a month by storms, most of the promised ships did not arrive at all. Louis and his associates claimed the ships for themselves, while the rest of the army had to resume the long march to Antioch. The army was almost entirely destroyed, either by the Turks or by sickness.
Louis eventually arrived in Antioch on March 19 after being delayed by storms, Amadeus of Savoy had died on Cyprus along the way. Louis was welcomed by Eleanor’s uncle Raymond of Poitiers. Raymond expected him to help defend against the Turks and to accompany him on an expedition against Aleppo, but Louis refused, preferring instead to finish his pilgrimage to Jerusalem rather than focus on the military aspect of the crusade. Eleanor enjoyed her stay, but her uncle wanted her to remain behind and divorce Louis if the king refused to help him. Louis quickly left Antioch for Tripoli. Meanwhile, Otto of Freising and the remnant of his troops arrived in Jerusalem early in April, and Conrad soon after. Fulk, Patriarch of Jerusalem, was sent to invite Louis to join them. The fleet that had stopped at Lisbon arrived around this time, as well as the Provençals who had left Europe under the command of Alfonso Jordan, Count of Toulouse. Alphonso himself did not make it to Jerusalem as he died at Caesarea. He was supposedly poisoned either by Eleanor of Aquitaine or Raymond II of Tripoli, the nephew who feared his political aspirations in the county. The original focus of the crusade was Edessa, but the preferred target of King Baldwin III and the Knights Templar was Damascus.
Some of the barons native to Jerusalem pointed out that it would be unwise to attack Damascus, as the Burid dynasty, though Muslim, were their allies against the Zengid dynasty. Conrad, Louis, and Baldwin insisted, Damascus was a holy city for Christianity. Like Jerusalem and Antioch, it would be a noteworthy prize in the eyes of European Christians. In July their armies assembled at Tiberias and marched to Damascus, around the Sea of Galilee by way of Banyas. There were perhaps 50,000 troops in total.
According to William of Tyre, on 27 July the crusaders decided to move to the plain on the eastern side of the city, which was less heavily fortified but had much less food and water. It was recorded by some that Unur had bribed the leaders to move to a less defensible position, and that Unur had promised to break off his alliance with Nur ad-Din if the crusaders went home. Meanwhile Nur ad-Din and Saif ad-Din had by now arrived. With Nur ad-Din in the field it was impossible to return to their better position. The local crusader lords refused to carry on with the siege, and the three kings had no choice but to abandon the city. First Conrad, then the rest of the army, decided to retreat back to Jerusalem on 28 July, though for their entire retreat they were followed by Turkish archers who constantly harassed them.
Each of the Christian forces felt betrayed by the other. A new plan was made to attack Ascalon and Conrad took his troops there, but no further help arrived, due to the lack of trust that had resulted from the failed siege. This mutual distrust would linger for a generation due to the defeat, to the ruin of the Christian kingdoms in the Holy Land. After quitting Ascalon, Conrad returned to Constantinople to further his alliance with Manuel. Louis remained behind in Jerusalem until 1149.
Back in Europe, Bernard of Clairvaux was humiliated by the defeat. Bernard considered it his duty to send an apology to the Pope and it is inserted in the second part of his Book of Consideration. There he explains how the sins of the crusaders were the cause of their misfortune and failures. When his attempt to call a new crusade failed, he tried to disassociate himself from the fiasco of the Second Crusade altogether. He would die in 1153.
The Wendish Crusade achieved mixed results. While the Saxons affirmed their possession of Wagria and Polabia, pagans retained control of the Obodrite land east of Lübeck. The Saxons also received tribute from Chief Niklot, enabled the colonization of the Bishopric of Havelberg, and freed some Danish prisoners. However, the disparate Christian leaders regarded their counterparts with suspicion and accused each other of sabotaging the campaign. In Iberia, the campaigns in Spain, along with the siege of Lisbon, were some of the few Christian victories of the Second Crusade. They are seen as pivotal battles of the wider Reconquista, which would be completed in 1492.
In the East the situation was much darker for the Christians. In the Holy Land, the Second Crusade had disastrous long-term consequences for Jerusalem. Damascus no longer trusted the crusader kingdom, and the city was handed over to Nur ad-Din in 1154. Baldwin III finally seized Ascalon in 1153, which brought Egypt into the sphere of conflict. Jerusalem was able to make further advances into Egypt, briefly occupying Cairo in the 1160s. However, relations with the Byzantine Empire were mixed, and reinforcements from Europe were sparse after the disaster of the Second Crusade. King Amalric I of Jerusalem allied with the Byzantines and participated in a combined invasion of Egypt in 1169, but the expedition ultimately failed. In 1171, Saladin, nephew of one of Nur ad-Din's generals, was proclaimed Sultan of Egypt, uniting Egypt and Syria and completely surrounding the crusader kingdom. Meanwhile the Byzantine alliance ended with the death of emperor Manuel I in 1180, and in 1187, Jerusalem capitulated to Saladin. His forces then spread north to capture all but the capital cities of the Crusader States, precipitating the Third Crusade.