Relations between the crusaders and Byzantium declined steadily over the course of the first four Crusades. Although it could be argued that poor relations were first formed following the Great Schism in 1054, when the Eastern and Western Churches first separated and excommunicated each other, relations between Byzantium and the west were relatively strong during the First Crusade and only really worsened after Dorylaeum. After 1095, however, relations gradually became worse as the Byzantines provided even less support to the Crusaders and the breakdown in relations ultimately resulted in the sack of Byzantium in 1204.
Pope Urban II officially announced the First Crusade as a result of the Byzantine Emperor’s plea for military assistance; the Church owed an allegiance to Alexius Comnenus to defend the Empire from the Seljuk attack. Though, as Alexius had only requested a small army of 500 knights, his plea should be treated as more of a catalyst and a minor motive behind the First Crusade. Urban took advantage of the troubles in Asia Minor in order to go ahead with the Crusade, with its aim of reclaiming the Holy Land for Christendom. Not quite ready to supply this number of people as they traversed his territories, the emperor saw his Balkan possessions subjected to further pillage at the hands of his own allies.[38] Alexios dealt with the first disorganized group of Crusaders, led by the preacher Peter the Hermit, by sending them on to Asia Minor, where they were massacred by the Turks in 1096. Once the second, stronger wave of crusaders reached Byzantium, it is clear that there were more significant divisions; Alexius attempted to secure an oath of loyalty from the crusade leaders in return for his financial and diplomatic support, though many disrespectfully refused to sign his oath of vassalage. For example, Raymond of Toulouse would only agree to a modified oath, which isolated him from some of the other leaders and also meant that he appeared to have little loyalty to Alexius. Other leaders who begrudged Alexius’ oath included Baldwin of Boulogne and Godfrey of Bouillon, who both refused outright to sign, as well as Tancred of Hauteville, who eventually agreed to, but broke the oath. As well as refusing to sign his oath, several of the leaders had also attacked the Byzantine Empire at some point or other, which led to difficult relations- in particular, Bohemond, who had led attacks against Alexius including at Darazzo. Neverthless, the crusade was a notable success for Byzantium, as Alexios recovered a number of important cities and islands. The siege of Nicaea by the crusaders forced the city to surrender to the emperor in 1097, and the subsequent crusader victory at Dorylaeum allowed the Byzantine forces to recover much of western Asia Minor, including Rhodes, Ephesus, Chios and Smyrna. This success is ascribed by Alexios’ daughter, Anna, to his policy and diplomacy, but by the Latin historians of the crusade to his treachery and deception. In 1099, a Byzantine fleet of ten ships was sent to assist the crusaders in capturing Laodicea and other coastal towns as far as Tripoli. However, most of the leaders who had not attacked Byzantium or sought to claim land on the crusade were simply responding to Urban’s claim of plenary indulgence (remission of sins) rather than crusading for purely deontological, spiritual reasons. When Alexius’ army, which was supposed to be a relief force including Taticius, turned back’ from helping the crusade armies who were besieged at Antioch, Bohemond claimed the city under the grounds that Alexius had forfeited all rights by deserting them. This of course angered Alexius and made relations even worse, only being resolved at the Treaty of Devol in 1108, which made Bohemond a vassal of Alexius.
The call to arms of the Second Crusade was much less driven by the influence of Byzantium, rather by the Fall of Edessa to the army of Zenghi. After the crusader army’s victory at the Battle of Dorylaeum in 1097, Alexius’ forces retreated to Nicaea, signifying the end of their support of the crusader armies. Relations between the Crusader States and Byzantium subsequently deteriorated towards the end of Alexius’ reign, and his succeeding son, Manuel Comnenus, pursued a much weaker diplomatic relationship with the West. The first real test of Manuel’s reign came in 1144, when he was faced with a demand by Raymond, Prince of Antioch for the cession of Cilician territories. However, following the capture of Antioch Raymond realized that immediate help from the west was out of the question and thus had to prepare for a humiliating visit to Byzantium to ask for the protection of the Emperor. After submitting to Manuel, he was promised the support that he had requested, and his allegiance to Byzantium was secured. Manuel had his own national interests in mind, however, and subsequently formed an alliance with Nur-ad-Din against Kilij Arslan, the Sultan of Rum- he was therefore unable to provide much support to the crusader states during this period. While on campaign in Konya, Manuel received a letter from Louis VII of France announcing his intention of leading an army to the relief of the crusader states. In 1147 he granted a passage through his dominions to two armies of the Second Crusade under Conrad and Louis, though annoyed that they did not provide official papal legates. Byzantine troops followed the Crusaders all the way, attempting to police their behaviour, and further troops were assembled in Constantinople, ready to defend the capital against any acts of aggression. Manuel took the precaution- which his grandfather, Alexios, had not taken- of making repairs to the city walls, and he pressed the two kings for guarantees concerning the security of his territories. By 1148 Manuel had seen the benefits of securing an alliance with Conrad, whose sister-in-law, Bertha, he had earlier married; he actually persuaded the German king to renew their alliance against Roger of Sicily- though this only created logistical issues for Louis’ contingent; the army was bound not to use Rodger’s fleet and Manuel also provided too few ships, thus they were subsequently forced to walk to the Holy Land. Unfortunately for the Byzantine emperor, Conrad died in 1152, and despite repeated attempts, Manuel could not reach an agreement with his successor, Frederick Barbarossa who subsequently fought his way through Anatolia at Dhidimotikon in November 1189. Manuel had admittedly provided some help to the crusaders during the Second Crusade, however, his guides had failed to open enough local markets to the crusaders, other than expensive markets that drained finances, and also passed on their positions to the Seljuk Turks. Manuel’s lack of help for the crusaders and his mistrust ultimately resulted in a long-term schism between Europe and Byzantium. In addition, the Byzantine Emperor was provoked to march into Antioch in 1158, after Reynald of Antioch had the Byzantine governor of Cyprus brutally killed in 1156.
Manuel Comnenus died in 1180, and was replaced first by Alexius II, then by Andronikus in 1183, who was equally uninterested in establishing strong Byzantine-crusader relations, which were only further weakened following Richard I’s pillaging and seizure of Cyprus, which was held by relatives of the Byzantine Emperor. The effects of Bernard’s Apologia after the Second Crusade moreover meant that many Europeans were reluctant to go on another Crusade and the small contingents that were travelling to Outremer were certainly not substantial enough to weaken the Muslim forces- support from Byzantium was perhaps therefore of the utmost importance at this time, though it was non-existent. Even following the crusaders’ devastating defeat at the Battle of Hattin, Andronikus did nothing to prevent the fall of the kingdom of his still allies.
The unfortunate events of the Fourth Crusade, where Constantinople was sacked, was a result of the Frankish army, but Pope Innocent III tried to prevent the events from happening by threatening excommunication to those who attacked fellow Christians. The disapproval of the attacks on Constantinople by the Pope, who was the supreme authority of the crusades, emphasizes that the Franks were not supposed to view the Byzantines as enemies and that there were many who were in full support of the Orthodox Christians. The Franks were eager to put Prince Alexius, who was more western in culture, on the thrown of the eastern empire. Many Franks felt he would implement policies that would favor their goals and that he should claim the throne that was rightfully his, as well as foolishly promising to pay off the crusader debts. However, soon after being crowned emperor, he discovered that he did not have sufficient funds to uphold the promises he made. The willingness of the Franks to attack Christians and postpone their travels to the Holy Lands, which was the purpose of the Fourth Crusade, describes how deteriorated the relations between the two powers had become. To the dismay of the Byzantines, the Franks became ever more agitated by Alexius’ inability to pay-up and subsequently convinced themselves that they were heretics due to their disobedience of Rome. Thus, the sack of Constantinople brought the Fourth Crusade to a screeching halt and hampered the overall potential for the crusades to have any lasting effect.
In conclusion, the Franks and Byzantines had a complicated and strained relationship with each other, regardless of the fact that the crusades were supposed to create unity between them. The disagreements began long before the crusades with the Great Schism, but ultimately deteriorated into a complete lack of co-operation between Europe and Byzantium. Even with their differences, the Byzantines and Franks officially supported each other throughout the crusades and they were able to work together at times as allies. When Alexius made the Frankish leaders swear fealty to him, he also rewarded them- even Bohemond, an enemy of Alexius was given a sum of money for example, thus displaying the gratitude Alexius had toward the armies that showed up to fight for him. Moreover, when Pope Urban II called for the First Crusade at Clermont in 1095 all the chronicles show that he had a goal to help the Orthodox Christians in the east. At the beginning of the crusades, it was actually feasible to think that the Catholics and Orthodox churches could reunite and forget the Schism, proving that their differences were able to be settled- unfortunately, however, this was simply unachievable.