First Crusade - East at the end of the 11th century

Eastward of Western Christendom nearest neighbor was Eastern Christendom: the Byzantine Empire, a Christian Empire which had severed its links with the Pope of Rome, whose authority ceased to be recognised explicitly since the schism of 1054 (indeed, never has had accepted more than as a primum inter pairs next to the Patriarchs). Subtle dogmatic differences (the filioque clause and the Eucharist acimita or procimita) allowed to define the opposition between the Catholic Western Church and the Eastern Orthodox Church. The latest military defeats of the Byzantine Empire against their neighbours had provoked a deep instability that would only solve with the ascent to power of general Alejo I Comneno as basileus (Emperor). Under his reign, the Empire was confined to Europe and the West coast of Anatolia, and faced many enemies, the Normans to the West and the Seljuk Turks to the East. Further East, Anatolia, Syria, Palestine and Egypt were under Muslim control, although to some extent fragmented by cultural issues at the time of the first crusade. This fact contributed to the success of this campaign.
Mapa del Califato Omeya en el momento de su máxima extensión.Map of the Umayyad Caliphate at the time of its greatest extent.

Anatolia and Syria were under the control of the Seljuk Turks, Sunnis, who had formerly formed a great empire, but at that time were divided into smaller States. The sultan Alp Arslan defeated the Byzantine Empire at the battle of Manzikert, in 1071, and had managed to incorporate much of Anatolia to the Empire. However, the Empire was divided after his death the following year. Alp Arslan succeeded Malik Shah I and continue reigning until 1092, period in which the Seljuk Empire would face internal rebellion. In the Sultanate of Rüm in Anatolia, Malik Shah I was succeeded by Kilij Arslan I, and in Syria by his brother Tutush I, who died in 1095. The sons of the latter, Ridwan and Duqaq, inherited Aleppo and Damascus respectively, further dividing Syria between different Emirs faced each other and faced also with Kerbogha, the atabeg of Mosul. All these States were more concerned to maintain their own territories and in control of their neighbors than to cooperate between them for addressing the threat cross.
Elsewhere in what was nominally territory Seljuk had become also the ortoqid dynasty. In particular, this new dynasty controlled Northwestern Syria and northern Mesopotamia, and also controlled Jerusalem until 1098. To the East of Anatolia and Northern Syria was founded a new State, which would become known as the dynasty of the danishmends for having been founded by a mercenary known as the Danishmends Seljuk-driven. The Crusaders did not have any significant contact with these groups until after the crusade. Finally, also should take into account the Hashshashin, who by then were beginning to have some relevance in Syrian Affairs.
Imperio bizantino y los Estados Cruzados después de la Primera Cruzada.Byzantium and the Crusader States after the first crusade.
While the region of Palestine was under Persian rule and during the first Islamist, Christian pilgrims were, in general, properly treated. One of the first Islamic rulers, Caliph Umar ibn al - Jattab, allowed Christians to carry out all their rituals except for any kind of celebration in public. However, at the beginning of the 11th century, the Fatimid Caliph al-Huséin al - Hakim Bi - Amr Allah began to persecute Christians in Palestine, persecution that would lead, in 1009, the destruction of the holiest temple for them, the Church of the Holy Sepulchre. It later softened the measures against Christians and, instead of pursuing them, created a tax for all confession pilgrims who wanted to enter Jerusalem. However, the worst was yet to come: A group of Muslim Turks, the Seljuks, very powerful, aggressive and fundamentalist in terms of interpretation and compliance with the precepts of Islam, began his rise to power. The Seljuks saw Christian pilgrims as polluters of faith, so they decided to finish with them. At that time they began to arise stories full of barbarism on the treatment to the pilgrims, who were going from mouth in mouth to Western Christendom. These stories, however, instead of deterring pilgrims, made the trip to the Holy Land is dye a much more sacred aura that already had previously.
La derrota de la cruzada de los pobres.The defeat of the people's crusade.
Egypt and much of Palestine were under the control of the Fatimid caliphate, Arab and Shia branch of Islam. His empire was significantly smaller since the arrival of the Seljuk Turks, and Alejo I went on to advise the Crusaders that they work together with the Fatimids to face their common enemy, the Seljuks. By then, the Fatimid caliphate was ruled by the Caliph al - Musta'sim ' li (although the real power was in the hands of the vizier Al - Afdal Shahanshah), and having lost the city of Jerusalem against the Seljuk Turks in 1076, had recaptured it from the hands of the northerly in 1098, when the Crusaders were already underway. The Fatimids, at first, did not consider the Crusaders as a threat, since they thought that they had been sent by the Byzantines, and they contentarían with the capture of Syria, which would leave quiet Palestinian. Not sent an army against the Crusaders until these did not come to Jerusalem.
Godfrey of Bouillon as Protector of Jerusalem. His official title was Advocatus Sancti Sepulchri, "Protector of the Holy Sepulchre".

Source: Primera Cruzada – Oriente a finales del siglo XI