Crusade is not a contemporaneous term: instead the terms iter for journey or peregrinatio for pilgrimage were used. Not until the word crucesignatus for one who was signed with the cross was adopted at the close of the twelfth century was specific terminology developed. The Oxford English Dictionary links the etymology of the word crusade to the modern French croisade, Old French croisee, Provençal crozada, Spanish cruzada, Italian/medieval Latin crociata based on the verb "to cross," "a being crossed," "a crossing" or "marking with the cross," "a taking the cross." The Middle English equivalents were derived from old French; croiserie in the 13th–15th centuries and croisee in the 15–17th century. "Croisade" appeared in English c1575, and continued to be the leading form till c1760. By convention historians adopt the term for the Christian holy wars from 1095 but this does lead to a misleading impression of coherence in the early "Crusades".
The Crusades in the Holy Land are traditionally counted as nine distinct campaigns, numbered from the First Crusade of 1095–99 to the Ninth Crusade of 1271/2. This convention is used by Charles Mills in his History of the Crusades for the Recovery and Possession of the Holy Land (1820), and is often retained for convenience, even though it is somewhat arbitrary: The Fifth and Sixth Crusades led by Frederick II may be considered a single campaign, as can the Eight Crusade and Ninth Crusade led by Louis IX.
Usage of the term "crusade" may differ depending on the author. Giles Constable describes four different perspectives among scholars:Traditionalists restrict their definition of crusades to the Christian campaigns in the Holy Land, "either to assist the Christians there or to liberate Jerusalem and the Holy Sepulcher", during 1095–1291.Pluralists use the term crusade of any campaign explicitly sanctioned by the reigning Pope. This reflects the view of the Roman Catholic Church (including medieval contemporaries such as Saint Bernard of Clairvaux) that every military campaign given Papal sanction is equally valid as a crusade, regardless of its cause, justification, or geographic location. This broad definition subsumes attacks on paganism and heresy, such as the Albigensian Crusade, the Northern Crusades and the Hussite Wars, and wars for political or territorial advantage, such as the Aragonese Crusade in Sicily, a crusade declared by Pope Innocent III against Markward of Anweiler in 1202, one against the Stedingers, several (declared by several popes) against Emperor Frederick II and his sons, two crusades against opponents of King Henry III of England, and the Christian re-conquest of Iberia.Generalists see crusades as any and all holy wars connected with the Latin Church and fought in defence of their faith.Popularists limit the crusades to only those that were characterised by popular groundswells of religious fervour – that is, only the First Crusade and perhaps the People's Crusade.
Medieval Muslim historiographers such as Ali ibn al-Athir refer to the Crusades as the "Frankish Wars" (ḥurūb al-faranǧa حروب الفرنجة). The term used in modern Arabic, ḥamalāt ṣalībiyya حملات صليبية, lit. "campaigns of the cross", is a loan translation of the term crusade as used in Western historiography.
In the seventh and eighth centuries, Islam was introduced in the Arabian Peninsula by the Islamic prophet Muhammad and a newly unified polity. This led to a rapid expansion of Arab power, the influence of which stretched from the northwest Indian subcontinent, across Central Asia, the Middle East, North Africa, southern Italy, and the Iberian Peninsula, to the Pyrenees. Tolerance, trade, and political relationships between the Arabs and the Christian states of Europe waxed and waned. For example, the Fatimid caliph al-Hakim bi-Amr Allah destroyed the Church of the Holy Sepulchre in Jerusalem, but his successor allowed the Byzantine Empire to rebuild it. pilgrimages by Catholics to sacred sites were permitted, Christians resident in Muslim territories were given certain legal rights and protections under dhimmi status, were allowed to maintain their churches and interfaith marriages were not uncommon. Cultures and creeds coexisted and competed, but Catholic pilgrims and merchants reported that the frontier conditions between the Syrian ports and Jerusalem were increasingly inhospitable.
The Reconquista, the recapture of the Iberian peninsula from the Muslims, began during the 8th century, reaching its turning point in 1085 when Alfonso VI of León and Castile retook Toledo from Muslim rule. The Byzantine Empire also regained territory at the end of the 10th century, with Basil II spending most of his half-century reign in conquest. In Northern Europe, the Germans used crusading as a method to expand Christianity and their territories at the expense of the non-Christian Slavs, and Muslim Sicily was conquered by Norman adventurer Roger De Hauteville in 1091.
Europe in this period was immersed in power struggles on many different fronts. In 1054, centuries of attempts by the Latin Church to assert supremacy over the Patriarchs of the Eastern Empire led to a permanent division in the Christian church called the East–West Schism. Following the Gregorian Reform an assertive, reformist papacy attempted to increase its power and influence. Beginning around 1075 and continuing during the First Crusade, the Investiture Controversy was a power struggle between Church and state in medieval Europe over whether the Catholic Church or the Holy Roman Empire held the right to appoint church officials and other clerics. Antipope Clement III was an alternative pope for most of this period, and Pope Urban spent much of his early pontificate in exile from Rome. The result was intense piety, an interest in religious affairs, and religious propaganda advocating a just war to reclaim Palestine from the Muslims. The majority view was that non-Christians could not be forced to accept Christian Baptism or be physically assaulted for having a different faith, although a minority believed that vengeance and forcible conversion were justified for the denial of Christian faith and government. Participation in such a war was seen as a form of penance that could counterbalance sin.
The status quo was disrupted by the invading Turks. Historians once, but no longer, consider the 1071 victory over the Byzantine army at the Battle of Manzikert as a decisive moment but it did presage significant expansion of Great Seljuk Empire into nearly all of Anatolia. One year later the Turks wrested control of Palestine from the Fatimids.
In 1095 at the Council of Piacenza, Byzantine Emperor Alexios I Komnenos requested military aid from Pope Urban II to fight the Turks, probably in the form of mercenary reinforcements. It is likely he exaggerated the danger facing the Eastern Empire while making his appeal. At the Council of Clermont later that year, Urban raised the issue again and preached for a crusade. Historian Paul Everett Pierson asserts that Urban also hoped that aiding the Eastern Church would lead to its reunion with the Western under his leadership.
Almost immediately thereafter Peter the Hermit began preaching to thousands of mostly poor Christians, whom he led out of Europe in what became known as the People's Crusade. Peter had with him a letter he claimed had fallen from heaven instructing Christians to seize Jerusalem in anticipation of the apocalypse. In addition to the motivations of the landed classes, academic Norman Cohn has identified a "messianism of the poor" inspired by an expected mass apotheosis at Jerusalem. In Germany the Crusaders massacred Jewish communities. The Rhineland massacres were the first major outbreak of European antisemitism. In Speyer, Worms, Mainz and Cologne the range of anti-Jewish activity was broad, extending from limited, spontaneous violence to full-scale military attacks. Despite Alexios' advice to await the nobles, the People's Crusade advanced to Nicaea and fell to a Turkish ambush at the Battle of Civetot, from which only about 3,000 crusaders escaped.
Both Philip I of France and Emperor Henry IV were in conflict with Urban and did not participate. However, members of the high aristocracy from France, western Germany, the Low countries and Italy were drawn to the venture, commanding their own military contingents in loose, fluid arrangements based bonds of lordship, family, ethnicity and language. Foremost amongst these was the elder statesman, Raymond IV, Count of Toulouse. He was rivalled by the relatively poor but martial Bohemond of Taranto and his nephew Tancred from the Norman community of southern Italy. They were joined by Godfrey of Bouillon and his brother Baldwin I of Jerusalem leading a loose conglomerate from Lorraine, Lotharingia and Germany. These five Princes were pivotal to the campaign which was also joined by a Northern French army led by Robert Curthose, Stephen, Count of Blois and Robert II, Count of Flanders.
The armies including non-combatants may have contained as many as 100,000 people, travelled eastward by land to Byzantium where they were cautiously welcomed by the Emperor. Alexius persuaded many of the princes to pledge allegiance to him and that their first objective should be Nicaea, which Kilij Arslan I had declared the capital of the Sultanate of Rum. Having already destroyed the earlier People's Crusade, the over confident Sultan left the city to resolve a territorial dispute enabling its capture after a Crusader siege and a Byzantine navel assault. This marked a high point in Latin and Greek co-operation and also the start of Crusader attempts to take advantage of political and religious disunity in the Muslim world. Crusader envoys sent to Egypt seeking an alliance.
The Crusades' first experience of the Turkish tactics of lightly armoured mounted archers was when an advanced party led by Bohemond and Duke Roberts was ambushed at Dorylaeum. The Normans resisted for hours before the arrival caused a Turkish withdrawal. After this the normadic Seljuks avoided the crusade. The factionalism amongst the Turks that followed the death of Malik Shah meant they did not provide a united opposition. Instead Aleppo and Damascus had competing rulers. The three month march to Antioch was arduous with numbers reduced by the attrition of staravation, thirst and disease, combined with the decision of Baldwin to leave with 100 knights in order to carve out his own territory in Edessa. The crusaders embarked on an eight-month siege of Antioch but lacked the resources to fully invest the city while the residents lacked the resources to repel the invaders. Eventually, Bohemond persuaded a tower guard in the city to open a gate and the crusaders entered, massacring the inhabitants and pillaging the city. Sunni Islam had now recognised the threat and the sultan of Baghdad sent a relief force led by the Iraqi general Kerbogha. No assistance was provided by the Byzantines who had been told by the deserting Stephen of Blois that the cause was lost. Losing numbers through desertion and starvation in the besieged city the crusaders attempted to negotiate surrender but this was rejected by Kerbogha who wanted to destroy them permanently. Morale within the city was boosted when Peter Bartholomew claimed to have discovered the Holy Lance. Bohemond recognised that the only option now was for open combat and launched a counterattack against the besiegers. Despite superior numbers Kerbogha's army, which was divided into factions and surprised by the motivation of the Franks, retreated and abandoned the siege. The Crusaders then delayed for months while they argued over who would have the captured territory. This only ended when news arrived that the Fatimid Egyptians had taken Jerusalem from the Turks and it became imperative to attack before they could consolidate their position. Bohemond remained in Antioch, retaining the city, despite his pledge that this would return to Byzantine control, while Raymond led the remaining crusader army rapidly south along the coast to Jerusalem. The Jewish and Muslim inhabitants fought together to defend Jerusalem, but the crusaders entered the city on 15 July 1099. They proceeded to massacre the inhabitants and pillage the city. In his Historia Francorum qui ceperunt Iherusalem, Raymond D'Aguilers exalted actions a modern viewpoint would consider atrocities.
The First Crusade established the first four Crusader states in the Eastern Mediterranean: the County of Edessa (1098–1149), the Principality of Antioch (1098–1268), the Kingdom of Jerusalem (1099–1291), and the County of Tripoli (1104—Tripoli was not conquered until 1109—to 1289). The Armenian Kingdom of Cilicia originated before the Crusades, but it received kingdom status from Pope Innocent III and later became fully Westernised by the House of Lusignan. According to historian Jonathan Riley-Smith, these states were the first examples of "Europe overseas". They are generally known as outremer, from the French outre-mer ("overseas" in English).
On a popular level, the First Crusade unleashed a wave of impassioned, pious Catholic fury—expressed in the massacres of Jews that accompanied the crusades and the violent treatment of the "schismatic" Orthodox Christians of the east. A second, less successful crusade known as the Crusade of 1101 followed in which Turks led by Kilij Arslan defeated the crusaders in three separate battles.
Under the papacies of Calixtus II, Honorius II, Eugenius III and Innocent II smaller scale crusading continued around the crusader states in the early 12th century. The third decade saw campaigns by Fulk V of Anjou, the Venetians, Conrad III of Germany and the foundation of the Knights Templar. The period also saw the innovation of granting indulgences to those who opposed papal enemies, and this marked the beginning of politically motivated crusades. The loss of Aleppo in 1128 and Edessa (Urfa) in 1144 to Imad ad-Din Zengi, governor of Mosul led to preaching for what subsequently became known as the Second Crusade. King Louis VII and Conrad III led armies from France and Germany to Jerusalem and also Damascus without winning any major victories. Bernard of Clairvaux, who had encouraged the Second Crusade in his preaching, was upset with the violence and slaughter directed towards the Jewish population of the Rhineland.
Christian princes continued to make gains In the Iberian peninsula such as the King of Portugal, Afonso I, retaking Lisbon and Raymond Berenguer IV of Barcelona conquering the city of Tortosa In Northern Europe the Saxons and Danes fought against Wends in the Wendish Crusade, although no official papal bulls were issued authorising new crusades. The Wends were finally defeated in 1162.
Saladin united the enemies of the Crusader States, retook Jerusalem and won the Battle of Hattinin 1187. According to Benedict of Peterborough, Pope Urban III died of deep sadness on 19 October 1187 on hearing of the defeat. His successor, Pope Gregory VIII, issued a papal bull named Audita tremendi that proposed a further crusade later numbered the third to recapture Jerusalem. Frederick I, Holy Roman Emperor died en route to Jerusalem, drowning in the Saleph River, and few of his men reached the Eastern Mediterranean.
In transit to crusade, Richard I of England conquered Cyprus in 1191 in response to his sister and fiancee, who were travelling separately, being taken captive by the island's ruler, Isaac Komnenos. On arrival in the East, Richard quarreled with Philip II of France who returned home, leaving most of his forces behind and Leopold V, Duke of Austria. Richard recaptured Acre after a long siege, traveled south along the Mediterranean coast, defeated the Muslims near Arsuf and recaptured the port city of Jaffa. He twice advanced to within a days march of Jerusalem before judging that he lacked the resources to successfully capture the City. This marked the end of Richard's crusading career and was a calamitous blow to Frankish morale. A three-year truce was negotiated that allowed Catholics unfettered access to Jerusalem. Illness and politics in England forced Richard's departure, never to return, but Emperor Heny VI initiated the German Crusade to fulfil the promises made by his father, Frederick. Led by Conrad, Archbishop of Mainz, the army captured the cities of Sidon and Beirut. However, most of the crusaders returned to Germany when Henry died.
The thirteenth century saw popular outbursts of ecstatic piety in support of the Crusades such as the Children's Crusade in 1212. Large groups of young adults and children spontaneously gathered believing their innocence would enable success where their elders had failed. Little reliable evidence survives for these events. However, they provide an indication of how hearts and minds could be engaged for the cause.
Innocent III also began preaching what became the Fourth Crusade in 1200, primarily in France, but also in England and Germany. After gathering in Venice the crusade was used by Doge Enrico Dandolo and Philip of Swabia to further their secular ambitions. Dandolo's aim was expand Venice's power in the Eastern Mediterranean and Philip intended to restore his exiled nephew, Alexios IV Angelos, to the throne of Byzantium. The crusaders were unable to pay the Venetians for a fleet when too few knights arrived in Venice, so they agreed to divert to Constantinople and share what could be looted as payment. As collateral the crusaders seized the Christian city of Zara; Innocent was appalled, and excommunicated them. They also conquered Constantinople twice, after the initial success in taking the city, the original purpose of the campaign was defeated by the assassination of Alexios IV Angelos. In response the crusaders captured the Constantinople again and this time sacked it, pillaging churches and killing many citizens. The Fourth Crusade never came within 1,000 miles of its objective of Jerusalem.
The Fourth Crusade established a Latin Empire in the east and allowed the partition of Byzantine territory by its participants. The Latin emperor controlled one-fourth of the Byzantine territory, Venice three-eighths (including three-eighths of the city of Constantinople), and the remainder was divided among the other crusade leaders. This began the period of Greek history known as Frankokratia or Latinokratia ("Frankish [or Latin] rule"), when Catholic Western European nobles—primarily from France and Italy—established states on former Byzantine territory and ruled over the Orthodox Byzantine Greeks. In the long run, the sole beneficiary was Venice.
Following Innocent III's Fourth Council of the Lateran, crusading resumed in 1217 against Saladin's Ayyubid successors in Egypt and Syria for what is classified the Fifth Crusade. Led by Andrew II of Hungary and Leopold VI, Duke of Austria, forces drawn mainly from Hungary, Germany, Flanders, and Frisia achieved little. Leopold and John of Brienne besieged and captured Damietta but an army advancing into Egypt was compelled to surrender. Damietta was returned and an eight-year truce agreed. Frederick II, Holy Roman Emperor was excommunicated for breaking treaty obligations with the Pope to crusade. However his marriage to Isabella II of Jerusalem gave him a claim to the kingdom of Jerusalem and he finally arrived at Acre in 1228. Frederick was a most Muslim of Christian monarchs having grown up in Sicily, having a Muslim bodyguard and even a harem. His great diplomatic skills meant that the Sixth Crusade was largely negotiation supported by force. A peace treaty was agreed giving Latin Christians most of Jerusalem and a strip of territory from Acre, while the Muslims controlled their sacred areas. In return, an alliance was made with al-Kamil, Sultan of Egypt, against all of his enemies of whatever religion. The treaty and suspicions about Frederick's ambitions in the region made him unpopular and was forced to return to his domains when they were attacked by Pope Gregory IX. While the Empire and Papacy were in conflict it often fell to secular leaders to campaign. What is sometimes known as the Barons' Crusade was led by Theobald I of Navarre and Richard of Cornwall combining forceful diplomacy and the playing of rival Ayyubid factions off against each other. This brief renaissance for Frankish Jerusalem was illusory, being dependent on Ayyubid weakness and division following the death of Al-Kamil.
In 1244 a band of Khwarezmian mercenaries travelling to Egypt to serve As-Salih Ismail, Emir of Damascus, seemingly of their own volition, captured Jerusalem en-route and defeated a combined Christian and Syrian army at the La Forbie. Louis IX, king of France, organised a crusade, classified as the Seventh Crusade to attack Egypt in response, arriving in 1249. This was not a success. Louis was defeated at Mansura and captured as he retreated back to Damietta. Another truce was agreed for a ten-year period and Louis was ransomed. Louis remained in Syria until 1254 to consolidate the Crusader states. From 1265 to 1271, Baibars drove the Franks to a few small coastal outposts.
Late thirteenth century politics in the Eastern Mediterranean were complex with a number of powerful interested parties. The Mamluk sultan Baibars had three key objectives: the prevention of an alliance between the Latins and the Mongols, cause dissention between the Mongols particularly between the Golden Horde and the Persian Ilkhanate, and to maintain access to a supply of slave recruits from the Russian steppes. In this he developed diplomatic ties with Manfred, King of Sicily supporting him against the Papacy and Louis IX's brother Charles. The Crusader states were not unified and various powers competed for influence. Genoa and Venice fought the War of Saint Sabas. The Genoese were expelled from Acre and relocated to Tyre where they continued to trade happily with Bayber's Egypt. Indeed Baibers negotiated free passage for the Genoese with Michael VIII Palaiologos, Emperor of Nicaea who was newly restored to the rule of Constantinople.
The French, led by Louis IX's brother Charles of Anjou, similarly sought to expand their influence. In 1266, he seized Sicily, parts of the eastern Adriatic, Corfu, Butrinto, Avlona, and Suboto. He attempted to gain Byzantium politically through the Treaty of Viterbo. The heirs of Baldwin II of Constantinople and William II Villehardouin married Charles' children. If there were no offspring Charles would receive the empire and principality. Charles executed Conradin, great-grandson of Isabella I of Jerusalem and principal pretender to the throne of Jerusalem, when he seized Sicily from the Holy Roman Empire. When he purchased the rights to Jerusalem from Maria of Antioch, the surviving grandchild of Queen Isabella, he created a claim to rival that of Isabella's great grandson, Hugh III of Cyprus. Charles' planned crusade to restore the Latin Empire alarmed Michael VIII Palailogos. He delayed Charles by beginning negotiations with Pope Gregory X for union of the Greek and the Latin churches with Charles and Philip of Courtenay compelled to form a truce with Byzantium. Michael also provided Genoa with funds to encourage revolt in Charles' northern Italian territories.
In 1270, Charles turned his brother King Louis IX's last crusade to his own advantage, persuading Louis to ignore his advisers and direct the Eighth Crusade against Charles' rebel Arab vassals in Tunis. Louis' army was devastated by disease in the hot-summer Mediterranean climate, and Louis himself died at Tunis on 25 August. This ended the last significant crusading effort in the Eastern Mediterranean.
The 1281 election of a French pope, Martin IV, brought the full power of the papacy into line behind Charles. He prepared to launch a crusade with 400 ships carrying 27,000 mounted knights against Constantinople. But the fleet was destroyed in an uprising fomented by Michael VIII Palailogos and Peter III of Aragon. Peter was proclaimed king, and the House of Charles of Anjou was exiled from Sicily. Martin excommunicated Peter and called for a crusade against Aragon before Charles died in 1285, allowing Henry II of Cyprus to reclaim Jerusalem. Charles had spent his life trying to amass a Mediterranean empire, and he and Louis saw themselves as God's instruments to uphold the papacy.
One factor in the crusaders' decline was the disunity and conflict among Latin Christian interests in the eastern Mediterranean. Martin compromised the papacy by supporting Charles of Anjou, and tarnished its spiritual lustre with botched secular "crusades" against Sicily and Aragon. The collapse of the papacy's moral authority and the rise of nationalism rang the death knell for crusading, ultimately leading to the Avignon Papacy and the Western Schism. The mainland Crusader states of the outremer were extinguished with the fall of Tripoli in 1289 and Acre in 1291. Most remaining Latin Christians left for destinations in the Frankokratia or were killed or enslaved.
Crusades were expensive; as the number of wars increased, their costs escalated. Pope Urban II called upon the rich to help First Crusade lords such as Duke Robert of Normandy and Count Raymond of St. Gilles, who subsidised knights in their armies. The total cost to King Louis IX of France of the 1284–85 crusades was estimated at six times the king's annual income. Rulers demanded subsidies from their subjects, and alms and bequests prompted by the conquest of Palestine were additional sources of income. The popes ordered that collection boxes be placed in churches and, beginning in the mid-twelfth century, granted indulgences in exchange for donations and bequests.
The military orders such as the Knights Hospitaller and the Knights Templar, provided Latin Christendom's first professional armies in support of the Latin Kingdom of Jerusalem and the other Crusader states. The Hospitallers (Order of Knights of the Hospital of Saint John of Jerusalem) had been founded in Jerusalem before the First Crusade but greatly enlarged its Mission once the Crusades began. The Poor Knights of Christ (Templars) and their Temple of Solomon were founded around 1119 by a small band of knights who dedicated themselves to protecting pilgrims en route to Jerusalem.
The Hospitallers and the Templars became supranational organisations as Papal support led to rich donations of land and revenue across Europe. This in turn led to a steady flow of new recruits and the wealth to maintain multiple fortifications across the Outremer. In time this developed into autonomous power in the region.
After the fall of Acre the Hospitallers first relocated to Cyprus, conquered and ruled Rhodes (1309–1522), Malta (1530–1798) and continue in existence to the present day. In 1322 the king of France suppressed the Knights Templar, ostensibly for sodomy, magic and heresy, but probably for financial and political reasons.
According to Jonathan Riley-Smith the Kingdom of Jerusalem was the first experiment in European colonialism creating a 'Europe Overseas' or Outremer. The raising, transportation and supply of large armies led to flourishing trade between Europe and the outremer. The Italian city states of Genoa and Venice flourished, creating profitable trading colonies in the eastern Mediterranean. This trade was sustained through the middle Byzantine and Ottoman eras, and the communities were often assimilated and known as Levantines or Franco-Levantines.
The Crusades consolidated the papal leadership of the Latin Church, reinforcing the link between Western Christendom, feudalism and militarism manifesting itself in the habituating of the clergy to violence. This led to the legitimisation of seizing land and possessions from pagans on religious grounds and was debated through to the Age of Discovery in the 15th and 16th centuries. In addition the growth of the system of indulgences later was a catalyst for the Protestant Reformation in the early 16th century. The crusades also had a role in the creation and institutionalisation of the military and Dominican orders as well as the Medieval Inquisition.
This assertiveness and the behaviour of the crusaders appalled the Greeks and Muslims providing a lasting barrier between the Latin world and both the Islamic and Orthodox religions. This made the reunification of the Christian church impossible and created a perception of the Westerners of being both aggressors and losers.
Helen Nicholson argues that the increased contact between cultures the Crusades instigated improved the perception of Islamic culture. Alongside contact in Sicily and Spain the crusades led to knowledge exchange with Christians learning new ideas from the Muslims in literature and hygiene. The Muslims also had classical Greek and Roman texts in their libraries, allowing Europe to rediscover pre-Christian philosophy. In contrast the Muslim world took little from the Crusaders beyond military tactics and did not take any real interest in European culture until the 16th century. Indeed, the Crusades were of little interest to the Muslim world: there was no history of the crusades translated into Arabic until 1865 and no published work by a Muslim until 1899.
Jonathan Riley-Smith considers that much of the popular understanding of the crusades derives from the novels of Walter Scott and the French histories by Joseph François Michaud. The crusades provided an enormous amount of source material, stories of heroism and interest that underpinned growth in medieval literature, romance and philosophy.
Five major sources of information exist on the Council of Clermont that led to the First Crusade: the anonymous Gesta Francorum (The Deeds of the Franks, dated about 1100–01); Fulcher of Chartres, who attended the council; Robert the Monk, who may have been present, and the absent Baldric, archbishop of Dol and Guibert de Nogent. These retrospective accounts differ greatly. In his 1106–07 Historia Iherosolimitana, Robert the Monk wrote that Urban asked western Roman Catholic Christians to aid the Orthodox Byzantine Empire because "Deus vult" ("God wills it") and promised absolution to participants; according to other sources, the pope promised an indulgence. In these accounts, Urban emphasises reconquering the Holy Land more than aiding the emperor and lists gruesome offences allegedly committed by Muslims. Urban wrote to those "waiting in Flanders" that the Turks, in addition to ravaging the "churches of God in the eastern regions", seized "the Holy City of Christ, embellished by his passion and Resurrection—and blasphemy to say it—have sold her and her churches into abominable slavery". Although the pope did not explicitly call for the reconquest of Jerusalem, he called for military "liberation" of the Eastern Churches. After the 1291 fall of Acre, European support for the Crusades continued despite Criticism by contemporaries, such as Roger Bacon, who believed them ineffective: "Those who survive, together with their children, are more and more embittered against the Christian faith".
During the 16th-century Reformation and Counter-Reformation, Western historians saw the crusades through the lens of their own religious beliefs. Protestants saw them as a manifestation of the evils of the papacy, and Catholics viewed them as forces for good. Eighteenth-century Enlightenment historians tended to view the Middle Ages in general, and the crusades in particular, as the efforts of barbarian cultures driven by fanaticism. These scholars expressed moral outrage at the conduct of the crusaders and criticised the crusades' misdirection—that of the Fourth in particular, which attacked a Christian power (the Byzantine Empire) instead of Islam. The Fourth Crusade had resulted in the sacking of Constantinople, effectively ending any chance of reconciling the East–West Schism and leading to the fall of the Byzantine Empire to the Ottomans. In The History of the Decline and Fall of the Roman Empire Edward Gibbon wrote that the crusaders' efforts could have been more profitably directed towards improving their own countries. By the early Romantic period in the 19th century, that harsh view of the Crusades and their era had softened; scholarship later in the century emphasised specialisation and detail.
The 20th century produced three important histories of the crusades: by Steven Runciman, Rene Grousset and a multi-author work edited by Kenneth Setton. Historians in this period often echoed Enlightenment-era criticism: Runciman wrote during the 1950s, "High ideals were besmirched by cruelty and greed ... the Holy War was nothing more than a long act of intolerance in the name of God". According to Norman Davies, the crusades contradicted the Peace and Truce of God supported by Urban and reinforced the connection between Western Christendom, feudalism, and militarism. The formation of military religious orders scandalised the Orthodox Byzantines, and crusaders pillaged countries they crossed on their journey east. Violating their oath to restore land to the Byzantines, they often kept the land for themselves. David Nicolle called the Fourth Crusade controversial in its "betrayal" of Byzantium. Similarly, Norman Housley viewed the persecution of Jews in the First Crusade—a pogrom in the Rhineland and the massacre of thousands of Jews in Central Europe—as part of the long history of anti-Semitism in Europe.
With the increasing focus on gender studies in the early 21st century, studies have been published on the topic of "Women in the Crusades" specifically. An essay collection on the topic was published in 2001, under the title Gendering the Crusades. In an essay on "Women Warriors", Caspi-Reisfield comes the conclusion that "the most significant role played by women in the West was in maintaining the status quo", in the sense of noble women acting as regents of feudal estates while their husbands were campaigining. The presence of individual noble women in crusades has been noted, such as Eleanor of Aquitaine (who joined her husband, Louis VII). The presence of non-noble women in the crusading armies, as in medieval warfare in general, was mostly in the role of logistic support (such as "washerwomen"), while the occasional presence of women soldiers was recorded by Muslim historians.
The success of the First Crusade inspired 12th-century popes such as Celestine III, Innocent III, Honorius III and Gregory IX to call for military campaigns with the aim of Christianization of the more remote regions of northern and northeastern Europe. These campaigns are known as the Northern Crusades. The Wendish Crusade of 1147 saw Saxons, Danes and Poles enforce Catholic control over the tribes of Mecklenburg and Lusatia, Polabian Slavs (or "Wends"). Celestine III called for a crusade in 1193, but when Bishop Berthold of Hanover responded in 1198, he led a large army to defeat and his death. In response Innocent III issued a bull declaring a crusade and Hartwig of Uthlede, Bishop of Bremen along with the Brothers of the Sword brought all of the north-east Baltic under Catholic control. Konrad of Masovia gave Chelmno to the Teutonic Knights in 1226 as a base for crusade against the local Polish princes. The Livonian Knights were defeated by the Lithuanians so Gregory IX merged the remainder of the order into the Teutonic Order as the Livonian Order. By the middle of the century, the Teutonic Knights completed their conquest of the Prussians before conquering and converting the Lithuanians in the subsequent decades. The order also came into conflict with the Eastern Orthodox Church, Pskov Republic and Novgorod Republic. In 1240 the Novgorod army defeated the Swedes in the Battle of the Neva, and two years later they defeated the Livonian Order in the Battle on the Ice.
The Albigensian Crusade (1209–1229) was a campaign against heretics that Innocent III launched to eradicate Catharism, which had gained a substantial following in southern France. The Cathars were driven underground, and the County of Toulouse passed under the direct control of Capetian France with the Treaty of Paris of 1229.
The Bosnian Crusade (1235–1241) was a campaign against the Bosnian church, depicted as a campaign against Catharism (Bogomilism) although possibly motivated by a Hungarian territorial expansion. In 1216 a mission was sent to convert Bosnia to Rome but failed. In 1225, Honorius III called the Hungarians to undertake the Bosnian Crusade that failed when the Hungarians retreated following defeat by the Mongols at the Battle of Mohi. From 1234 Gregory IX encouraged further crusading but again the Bosniaks repelled the Hungarians.
In the Iberian peninsula Crusader privileges were given to those aiding the Templars, Hospitallers and the Iberian orders that merged with the orders of Calatrava and Santiago. The papacy declared frequent Iberian crusades and from 1212 to 1265, and the Christian kingdoms drove the Muslims back to the Emirate of Granada, which held out until 1492 when the Muslims and Jews were expelled from the peninsula.
Minor crusading efforts lingered into the 14th century; Peter I of Cyprus captured and sacked Alexandria in 1365 in what became known as the Alexandrian Crusade; his motivation was as much commercial as religious. Louis II led the 1390 Barbary Crusade against Muslim pirates in North Africa; after a ten-week siege, the crusaders signed a ten-year truce.
Several crusades were launched during the 14th and 15th centuries to counter the expansion of the Ottoman Empire. The first, in 1396, was led by Sigismund of Luxemburg, king of Hungary; many French nobles joined Sigismund's forces, including the crusade's military leader, John the Fearless (Son of the Duke of Burgundy). Sigismund advised the crusaders to focus on defence when they reached the Danube, but they besieged the city of Nicopolis. The Ottomans defeated them in the Battle of Nicopolis on 25 September, capturing 3,000 prisoners. In 1309, as many as 30,000 peasants gathered from England, northeastern France and Germany proceeded as far as Avignon but disbanded there.
There were many minor crusades, or attempted crusades, in the context of the Ottoman conquest of the Balkans in the late 14th to early 15th centuries. A failed crusade against Ottoman Tunisia was undertaken in 1390. After their victory at the Battle of Kosovo in 1389, the Ottomans had conquered most of the Balkans, and had reduced the Byzantine influence to the area immediately surrounding Constantinople, which they later proceeded to besiege. In 1393 the Bulgarian tsar Ivan Shishman had lost Nicopolis to the Ottomans. In 1394, Pope Boniface IX proclaimed a new crusade against the Turks, although the Western Schism had split the papacy. The enterprise culminated disastrously at Nicopolis. As the Ottomans pressed westwards Sultan Murad II destroyed the last Papal funded crusade at Varna on the Black Sea in 1444 and four years later crushed the last Hungarian expedition.
John Hunyadi and Giovanni da Capistrano organised a 1456 crusade to lift the siege of Belgrade. Æneas Sylvius and John of Capistrano preached the crusade, the princes of the Holy Roman Empire in the diets of Ratisbon and Frankfurt promised assistance, and a league was formed between Venice, Florence and Milan, but nothing eventually came of it. In April 1487, Pope Innocent VIII called for a crusade against the Waldensians of Savoy, the Piedmont, and the Dauphiné in southern France and northern Italy. The only efforts undertaken were in the Dauphiné, resulting in little change. Venice was the only polity to continue to pose a significant threat to the Ottomans in the Mediterranean, but it pursued the "crusade" mostly for its commercial interests, leading to the protracted Ottoman–Venetian Wars, which continued, with interruptions, until 1718. The final end of the Crusades as an at least nominal effort of Catholic Europe against Muslim incursion comes in the 16th century, when the Franco-imperial wars assumed continental proportions. Francis I of France sought allies from all quarters, including with German Protestant princes. In 1536 Francis entered into one of the capitulations of the Ottoman Empire with Suleiman the Magnificent also making common cause with the Sultan's North African vassals including Hayreddin Barbarossa.
The Hussite Wars, also known as the "Hussite Crusade", involved military action against the Bohemian Reformation in the Kingdom of Bohemia and the followers of early Czech church reformer Jan Hus, who was burned at the stake in 1415. Crusades were declared five times during that period: in 1420, 1421, 1422, 1427, and 1431. These expeditions forced the Hussite forces, who disagreed on many doctrinal points, to unite to drive out the invaders. The wars ended in 1436 with the ratification of the compromise Compacts of Basel by the Church and the Hussites.