Being the first European invasion on the Arab territories under Islam, the Crusades represent one of the essential stages in the Arab and Islamic history . Unlike the Eastern Roman Empire that enjoyed an effective sociopolitical structure as well as demographic and economic superiority, the Western Roman Empire dismantled into smaller and rather weaker states. The Eastern Empire also enjoyed an effective front line of defense of the Black Sea against attacks from the north The Germanic tribe, the Herules, who invaded Italy in 476 and occupied Rome, brought the Western Roman Empire to an end. During the 10th and the 11th centuries, Europe suffered of many wars due to the attacks of the Bulgarians, the Magyarians and the Normads. Magyar attacked Germany, Italy and France. In 1071, the Normans invaded southern Italy. Further, the Viking groups settled in France and Great Moravia had collapsed. Occident had been suffering a decay of trade and industry as well as a decline in agriculture, since land was withdrawn from cultivation as a direct result of many northern invasions along with the high taxation on the marginal land. Due to the Feudal System, nobles were allocated tracts of land and held accountable to only the king of their territory and the Pope himself.
In reality, this led to a system of serfdom and virtual slavery. The feudal lords began to exploit the workers and other resources for their own profit. Thus, life of the poor was miserable. People suffered constant wars, famines, poverty, ignorance, horrendous diseases and plagues. In consequence, an intense religious piety rose up in the late 11th century among the lay public. The contact with the prosperous Orient, through the trade caravans (that used to pass through the Arab lands carrying spices and other goods to the West), the pilgrimage to Jerusalem and the Andalusian universities spread the idea that there could be a better life in the Promised Land. In this regard, the Arabs charged large amounts of customs duties on the goods passing through their territories and interior conflicts among the Muslim kingdoms as well as the Seljuk expansion in Asia Minor had threatened the security of the Christian pilgrims in particular and the Eastern Roman Empire in general. The Eastern Empire was trapped between the Bulgarians who destroyed the Byzantine army in the Battle of Archialus in 917, and the Seljuks who penetrated Anatolia from the East. The advance of the Seljuks into Anatolia after the Battle of Malazgirt (1071) resulted in great losses to the Eastern Empire, both of peasant-soldiers and of territories.
The Crusades were directed against the Muslims for various religious, economic, as well as political and social reasons. Basically, there had been many religious reasons behind this invasion. There had been a desire for putting limits to the expansion of Islam as a new faith and a desire for unifying the entire world's churches under the Roman domination. On the other hand, the Crusaders alleged that the Muslims were persecuting the Christians, so, a war aiming at rescuing Christ's grave and the Holy Land from the Muslim hand was inevitable. This desire increased when the Byzantine Empire was defeated in the Battle of Manzikert against the Seljuks. In the economic regard, at first, the majority of the Crusade soldiers were essentially poor and severely deprived, especially due to famines and poverty that struck some European areas. They joined the military service with the hope of finding a better life in the Promised Land and obtaining remission of their sins. Also, the Italians at that time were mainly wealthy noble traders, so they had a passion for taking hold of the Islamic world's treasures and establishing markets in the Arab lands to avoid paying the large amounts of customs duties charged on the goods passing through the Arab territories. In the political and military regards, the weakness of the Arab world caused by the existence of two caliphates (Sunni Abbassid Caliphate in Baghdad and Shiite Fatimid Caliphate in Egypt) which led to turbulence of their internal conditions; the victory of the Franks over the Andalusians; and the internal conflicts that Europe suffered, all made the Pope decide to launch these wars so as to unify the Europeans.
The Abbasid Caliphate had declined due to –among other reasons–the domination of the Persians and Seljuk Turks, the negligence of the military affairs, the weakness of the Caliphs as well as the threatening dangers of the Tatars from the East and the Crusaders from the West. The Fatimid Period became feebler due to the weakness of Caliphs and the domination of 'the Great Viziers' of the entire affairs of the state. The Fatimid influence began to decrease in Bilad el-Sham (Greater Syria) and small kingdoms in Syria, Aleppo, Damascus, Homs, Hama and Lebanon broke off the Caliphate. In Syria, Nur-Ed-Din Mahmoud governed independently under the symbolic authority of the Abbasid Caliphate. Noticing the value of Egypt and the weakness of the Fatimid Caliphate, he seized the opportunity of the conflict between the two Fatimid viziers (Shawar and Dirgham) to interfere in Egypt's affairs.

The First Crusade

In response to the call of Urban II in the Council of Clermont in November 1095 urging all Christians to launch war against the Orient to take hold of the Holy Land, two Crusade campaigns were launched: the Public (Peasants') Campaign and Lords Campaign. Led by Peter the Hermit and consisting of thousands of poor peasants, criminals and bandits sharing the passion to invade the Muslim land and obtain treasures and remission of their sins, the Public Campaign reached Constantinople pillaging and damaging whatever they took hold of. After crossing the Bosporus, they were defeated by Seljuk Turks at Nicaea. In 1096, led by feudal French lords, the Lords Campaign defeated the Turks, captured Antioch in 491, and in 1099 took Jerusalem.
The Muslim soldiers had to refuge to Al-Aqsa Mosque, and followed by the Crusaders, they were severely slaughtered by the Crusaders who took the Dome of the Rock. Godfrey of Bouillon was elected King of Jerusalem and obtained the title of 'Guardian of the Holy Sepulcher'. Although the European feudal lords quarreled among themselves and with the Byzantine emperor, they managed to take Haifa and Qysaria in 494, Akko (Acre) in 497, Tripoli and Gabala in 503, and Sidon in 504. As a result of the First Crusade, several small Crusade states were created: the Kingdom of Jerusalem, the County of Edessa, the Principality of Antioch and the County of Tripoli. Eventually, the Muslims began to reunite under Imad al-Din Zingy who re-took Edessa in 1144, which led the Pope to call for a second Crusade.

The Second Crusade

When the Muslims under Imad al-Din Zingy recaptured Edessa in 1144, Bernard of Clairvaux (an influential French monk) called for a new Crusade that was led by Conrad III of Germany and Louis IX of France. Both the two leaders met in Asia Minor and marched towards Jerusalem. With the help of the army of Imad al-Din Zingy, this Crusade collapsed after its siege of Damascus failed and returned to Europe. Winning numerous victories over the Crusaders, Nur Al-Din Zingy (the son of Imad al-Din) took Antioch and Tripoli, then sent Shirkuh to take Damascus in 1154 appointing Saladin its governor. In Egypt, the vizier El-Afdal concentrated his efforts on securing the country's borders. Seizing the opportunity of the Fatimid Caliphate declination, and the conflict between the two Fatimid viziers (Shawar and Dirgham), Nur-el-Din Mahmoud thought of invading Egypt so as to siege the Crusaders between two claws, and he sent a military expedition led by Shirkuh. Dirgham tried to make strong relations with the Crusaders and the King of Jerusalem against Nur-ed-Din and Shawar. Finally, a peace treaty was signed between the Crusaders and Shirkuh that stipulated that the Crusaders and Shirkuh should leave Egypt to the Egyptians.
Still thinking of unifying the Muslims in Greater Syria and Egypt to be able to achieve victory over the Crusaders, Nur al-Din sent a campaign to Egypt led by Shirkuh and Saladin which at last could bring Egypt under Nur-al Din's control. Saladin was appointed Vizier of Egypt and formed an army to fight against the Crusaders. After the death of Nur-al Din, the Muslims struggled over his reign, thus the Crusaders seized the opportunity to occupy Damascus. Saladin succeeded in recapturing Damascus and putting it under his control together with Aleppo. Given the title of 'Sultan', Saladin established the Ayyubid State which replaced both the Fatimid and Zingy States. On the other front, the Crusaders, led by Raynald of Chatillon, captured Al-Karak (city in Jordan), controlling both the trade and pilgrimage routes. Although there was a truce made between the Crusaders and Saladin, the former violated it by attacking the pilgrims' caravans; and in response, the latter launched the Battle of Hattin.

The Third Crusade

The Third Crusade is sometimes referred to as the Kings' Crusade. After Jerusalem was taken from the Christians, Pope Gregory VIII called for a Crusade that was led by Holy Roman Emperor Frederick I (Barbarossa), Richard the Lionheart of England, and Philip Augustus of France. In 1190, Frederick drowned in Cilicia (in Asia Minor) and Richard became the leader of the expedition. Before reaching the Palestine, Richard captured Cyprus from the Byzantines in 1190. A year later, his forces captured the port of Acre and many Muslims were slaughtered. The Crusader army headed south along the coast of the Mediterranean Sea, defeating the Muslims near Arsuf and recapturing the port city of Jaffa. Being in sight of Jerusalem, Richard negotiated a treaty with Saladin.
At last, Saladin granted him the Treaty of Ramla in 1192 which stipulated that unarmed Christian pilgrims were permitted to visit Jerusalem while it remained under the Muslim control and the Latin Kingdom was to be reduced to a geopolitical coastal strip that extended from Tyre to Jaffa. Richard I died during fighting in Europe and never returned to Palestine. Saladin returned to Damascus, where he died of fever in 1193.

The Fourth Crusade

Initiated by Pope Innocent III, the Fourth Crusade was intended to strengthen the Crusader positions at Acre by invading the Palestine through Egypt. On their way to Acre, however, the Crusaders – prompted by their desire for loot and new lands to rule – decided to sack Constantinople, the capital of the Byzantine Empire establishing the Latin Kingdom of Constantinople, which lasted until 1261 and taking hold of the trade routes of the Mediterranean Sea. This is often seen as the final breaking point of the Great Schism between the Eastern Orthodox Church and Western Roman Catholic Church. The Fourth Crusade stayed in Constantinople and did not reach Egypt.

The Fifth Crusade 

Initiated by Pope Ernest III, the Fifth Crusade sought to recover the Holy Land. In the first phase, a crusader force from Austria and Hungary joined the forces of the King of Jerusalem and the Prince of Antioch. In the second phase, crusader forces attacked the center of the Muslim power in Egypt and captured Damietta in 1219, but the Muslims, led by Sultan Al-Kamil, held off the attackers, which resulted in a great number of crusader losses and the surrender of the army. At last, Al-Kamil agreed to an eight-year peace agreement with Europe.

The Sixth Crusade

In 1228, Frederick II of the Holy Roman Empire led the Sixth Crusade. Setting sail from Brindisi and landing in Palestine, he achieved unexpected success through diplomacy and negotiations: Jerusalem, Nazareth, and Bethlehem were delivered to the crusaders for a period of ten years. In 1229 after failing to conquer Egypt, Frederick II concluded a peace treaty with Al-Kamil, the ruler of Egypt, which allowed Christians to rule over most of Jerusalem, while the Muslims were given control of the Dome of the Rock and the Al-Aqsa Mosque. The peace brought about by this treaty lasted for about ten years. In 1244, after putting Jerusalem under siege, the Muslims under the leadership of as-Saleh (the son of Al-Kamil) regained control of the city.

The Seventh Crusade

After the Muslims recaptured Jerusalem in 1244, Louis IX of France (Saint Louis) organized a new expedition that attacked Egypt, leaving from the port of Aigues-Mortes in southern France. Early 1249, the expedition reached Damietta and occupied it, then proceeded to Cairo. Leaving from Damascus, the Muslim army led by Najm al-Din Ayyub reached Al-Mansurah (in Egypt). But, Najm died and his wife (Shajart al-Durr) concealed the news of his death so as not to bring turbulence and despair to the Muslim army. Succeeding him in the army leadership, his son, Turanshah, achieved victory over the Crusaders and the French king was captured and forced to pay a heavy ransom. Louis IX had concurred with Hulagu Khan (leader of the Mongolians) in that the former was to attack Egypt, while the latter Iraq, so as to prevent Egypt from aiding Muslims in Iraq and Greater Syria. Other Crusades were planned but never carried out. When the Muslims captured Acre in 1291, the Latin Kingdom of Jerusalem was ended.

Consequences of the Cusades in The East and the West

In Europe, as a result of the migration of millions of farmers and poor people to participate in the crusades, the Feudal system collapsed to the benefit of the European kings who restored the strength of their central power. In addition, social and political changes had been made in Europe, such as the emergence of the middle class (which contained freemen workers) as well as the religious groups who professionalized in warfare issues. Furthermore, the Crusades had many impacts on the economic level. Real estates had witnessed a price reduction due to the migration of millions of people.
Another impact was the imposition of new taxes to cover the expenditure of the military expeditions. Moreover, some European countries boomed economically on the basis that the trade activity replaced the agricultural, with some cities (such as Genoa, Venice, Pisa, Marseille and Barcelona) becoming trade centers. This led to the widening of the domains of banks, the renewal of trade routes as well as the establishment of regular-lined marine routes. As for the scientific development Europe witnessed as one of the impacts of the Crusades, the Muslims ushered the European thinking into more progressive systems and ideas in medicine, chemistry, pharmacy, biology, mathematics, geography and astronomy. When necessity called upon the Europeans to translate the early scientific product of Muslim scholars, an interest in the Arabic language had come into existence and schools teaching this language were consequently established.
Though failing in taking Jerusalem from the Muslims, the Crusades left behind various aftermaths on the Muslim World. Threatened by the Crusade danger and attempting to expel the invaders, the Muslims in both Egypt and Bilad al-Sham discovered how vital each one was for the other and a necessity for collaboration and unity between them emerged. More than 250 years of war in the Arab's land against enemies from the west (the Crusaders) and from the East (the Mongols) caused great destruction and the expenditure of great human and economic resources which led to the later decline in military, economic and social spheres.
The Arabs had to bring great amounts of slaves (Mamelukes) to fight against the Crusades and they later became a selective class that governed Egypt and Syria for centuries. Moreover, Islamic art and architecture made a great leap in Egypt and Bilad al-Sham. Citadels, Forts, mosques, hotels with distinctive military style that distinguished the architecture of the Ayyubid and the Mameluke Periods were established.