Any hope of normal relations between Constantinople and the West disintegrates as the crusading movement, motivated partly by a desire to recapture the holy city of Jerusalem, partly by the hope of acquiring new territory, increasingly encroaches on imperial preserves and frustrates Emperor Alexios' foreign policy, which is primarily directed toward the reestablishment of imperial authority in Anatolia.

His relations with Muslim powers are disrupted on occasion and former valued imperial possessions, such as Antioch, pass into the hands of arrogant Western princelings, who even introduce Latin Christianity in place of Greek.

Thus, it is during Alexios' reign that the last phase of the clash between the Latin West and the Greek East is inaugurated.

He does regain some control over western Anatolia; he also advances into the southeast Taurus region, securing much of the fertile coastal plain around Adana and Tarsus, as well as penetrating farther south along the Syrian coast.

Neither Alexios nor succeeding Komnenian emperors will be able to establish permanent control over the Latin crusader principalities, however.

Continual Latin (particularly Norman) attacks, constant thrusts from Muslim principalities, the rising power of Hungary and the Balkan principalities—all conspire to surround Byzantium with potentially hostile forces.

Even Alexios' diplomacy, whatever its apparent success, cannot avert the continual erosion that will ultimately lead to the Ottoman conquest.

The First Crusade is largely concerned with Jerusalem, a city which has not been under Christian dominion for for hundred and sixty-one years, and the crusader army refuses to return the land to the control of the East Roman Empire.

The status of the First Crusade as defensive or as aggressive in nature remains controversial.

The Crusaders, on arrival at Jerusalem, invest the city and capture it in July 1099, massacring many of the city's Muslim, Christian, and Jewish inhabitants.

The Crusaders declare the Kingdom of Jerusalem, which approximates the borders of the present Israeli state.

Their gains in Syria and Palestine enable them to establish fiefdoms under the suzerainty of the King of Jerusalem: the Principality of Antioch, the County of Edessa, and, soon after, the County of Tripoli.

The Muslim forces of Mosul and Damascus, the western emirates in the Hamadan fold, halt the Christian advance.

The old order in the East collapses as Christian crusaders slaughter Jews and Muslims alike and carve new states from the Seljuq and Fatimid realms in Syria and Palestine, and the Seljuq sultanate of Rüm (i.e., Rome), extends its empire throughout the former imperial lands of Anatolia.

The successful crusade had prompted a call for reinforcements from the newly established Kingdom of Jerusalem, and Pope Paschal II, successor to Pope Urban II (who will die before learning of the outcome of the crusade that he had called), urges a new expedition.

He especially urges those who have taken the crusade vow but have never departed, and those who had turned back while on the march, some of whom are already scorned at home and face enormous pressure to return to the east.

The First Crusade will be followed by the Second to the Ninth Crusades, but the gains made will last for less than two centuries.

It is also the first major step since the fall of the Western Roman Empire towards reopening international trade in the West.

Hasan-e Sabbah and other Isma'ilites in Iran have refused to recognize the new Fatimid caliph in Cairo and have transferred their allegiance to his deposed elder brother, Nizar, and the latter's descendants.

There thus will grow up the sect of the Nizari Isma'ilites, who are at odds with the Fatimid caliphs in Cairo and are also deeply hostile to the 'Abbasids.

The Nizaris will make many changes in Isma'ilite doctrine, the most significant, from the point of view of the outside world, being the adoption of terrorism as a sacred religious duty.

From Alamut, by the end of the eleventh century, Hasan, as grand master or leader of the sect, commands a chain of strongholds all over Iran and Iraq, a network of propagandists, a corps of devoted terrorists, and an unknown number of agents in enemy camps and cities.

The Seljuq sultanate's attempts to capture Alamut fail, and soon the Assassins are claiming many victims among the generals and statesmen of the 'Abbasid caliphate, including two caliphs.

(This group, joining with Sabbah's terrorists, becomes known in the West as Assassins, a designation that derives from the Arabic “hashashin”, meaning “users of hashish”, based on stories—unconfirmed in any Ismaili sources—related by Marco Polo and others that the group employs hallucinatory drugs to stimulate them to their murderous acts.)

The crusaders in 1100 gain control of Hebron.

Baldwin has during the past two years captured Samosata and …

…Suruç (Sarorgia) from the Muslims, and defeated a conspiracy by some of his Armenian subjects in 1098.

At the end of 1099, he had visited Jerusalem along with Bohemond I of Antioch, but he returns to Edessa in January, 1100.

Doge Vitale I Michiel had not initially urged Venetian support when Pope Urban II initiated the First Crusade, perhaps because he could not see the advantages to Venice of such an expedition.

When the Doge saw the European commitment to the First Crusade, he then understood the war’s economic importance.

In particular, he foresaw that it was vital to Venice’s trade advantage to participate in territorial conquest, lest these advantages inure to the benefit of other marine republics.

Two hundred and seven ships had sailed from Venice in July 1099 to support the First Crusade.

The Doge had appointed his son, Vitale Giovanni, and the Bishop of Castello, Enrico Contarini, as the fleet’s commanders.

The Venetian fleet in December 1099 had intercepted enemy ships  at Rhodes and sunk them.

The Venetian fleet embarks in the spring of 1100 towards the Levant, where Godfrey of Bouillon and his troops have in the meantime taken Jerusalem.

Enemy ships have cut off Godfrey’s ability to receive aid and he is forced to negotiate with the Venetians.

Venice in exchange for its services, obtains the right to maintain a quarter not subject to custom offices, taxes, or excise taxes in every conquered city or territory.

The crusaders, having captured Jerusalem and the Church of the Holy Sepulchre, have fulfilled the crusading vow, but there are many who had gone home before reaching Jerusalem, and many who had never left Europe at all.

When the success of the crusade becomes known, these people are mocked and scorned by their families and threatened with excommunication by the Pope.

Many crusaders who had remained with the crusade all the way to Jerusalem have also gone home; according to Fulcher of Chartres, there are in 1100 only a few hundred knights left in the newfound kingdom.

Godfrey himself only rules for one year, dying in July 1100.

Tancred attacks Haifa, whose Jewish citizens join with the Fatimids in a successful defense of the city.

Reprimanded for his failure, Tancred is told that he has made “a mockery of the God of the Christians.”

When the city finally falls on July 25, 1100, the crusading forces massacre the city's surviving Jews.

The town of Malatya, which guards one of the Cilician Gates through the Taurus Mountains, has by 1100 been captured by an Armenian soldier of fortune.

Reports have been received that the Malik Ghazi Danishmend (Danishmend Emir), Ghazi Gümüştekin of Sivas, is preparing an expedition to capture Malatia, and the Armenians seek help from Bohemond.

Afraid to weaken his forces at Antioch, but not wishing to avoid the chance to extend his domain northwards, Bohemond marches north in August 1100 with only three hundred knights and a small force of foot soldiers.

Failing to send scouting parties, they are ambushed by the Turks, and completely encircled at the Battle of Melitene.

Bohemond manages to send one soldier to seek help from Baldwin of Edessa, but is captured and laden with chains and confined in prison in Neo-Caesarea (modern Niksar), where he is to languish until 1103.

Baldwin aids in relieving the siege.

The Armenian ruler of the city, Gabriel, now recognizes Baldwin as overlord of the city.