Alexios I Komnenos had not attained the throne of the Byzantine Empire through the legitimate method of inheritance. He had seized the throne in a military coup in 1081. He was appointed as a general by Emperor Michael VII Doukas 1071. Since Alexios had served with distinction in campaigns against the Seljuk Turks, Nikephoros III Botaneiates, the next Emperor who took power in 1078, retained him as a general.
In 1081, Alexios was entrusted with a significant military to counter the Norman threat, but he used this military to besiege Constantinople. On 1 April 1081, Alexios and his men broke through the walls of Constantinople and sacked the city. Botaneiates was forced to abdicate and retire into a monastery where he spent the rest of his life as a monk.
Alexios became the emperor but a significant part of the Byzantine political establishment despised him. They viewed him as a traitor who had usurped the throne through a coup. During his reign, Alexios was battling external threats from the Seljuk Turks and other Islamic forces and internal threats from his enemies in Constantinople. He tried to straighten his grip on power by promoting family members to key positions.
By the 1090s, his position in Constantinople had become precarious. He could not be sure of the loyalties of even his family members. Since he could trust no one in his kingdom, he had to look westwards to save his throne. In 1095, he sent his envoys to Pope Urban II to plead for military assistance.
If Alexios needed military assistance then why did he choose to plead before the Pope, the leader of a religious institution that does not maintain a military. Alexios had connections with the monarchies of Western Europe. He could have asked for military assistance from them. But he didn’t.
Alexios did not want a real military from Western Europe to march into the Levant. He knew that if he allowed the European monarchs to march into the Levant with their military, then his days as emperor would be numbered. Once the European monarchs became aware of the factionalism in Byzantine politics and his weak position, they would be tempted to usurp his throne. He thought that the Pope’s crusaders would pose less threat to his regime than with the militaries owned by the European monarchs.
In response to Alexios’s plea for assistance, Pope Urban II gave a call for a crusade for freeing the Holy Land. The ostensible purpose of the First Crusade was to free the Holy Land; the real purpose was to save Alexios’s throne from his rivals in Constantinople.