The Crusades, or the fact of giving a religious meaning to the fights that, all along the Middle Ages, happened between Christian and Muslim princes, led somehow to the internationalization of warfare. The first action related to the idea of Crusade was in the Spain of the "Reconquista". Alfonso VI of Castille, after his crushing defeat in Zalaca against the Almoravids, asks for help from foreign knights to defend Toledo and the Tajo basin against the continuous Muslim attacks.
The Crusades' origins come from an spontaneous feeling from pilgrims to Holy Places. They went there more and more often in armed groups, although the tolerant Arabs did not oppose any obstacle to them. This feeling was used by the pope Urban II, who preached for the first Crusade in 1095, with the aim to deviate the warlike actions of feudal lords. Besides, this way he would show a force exhibition to his weakened enemy, the Eastern Orthodox Church, as mercenaries went sent as aid for the Byzantine Empire. It had an extraordinary success, thousands of crusaders from all over Europe gathered in Constantinople and conquered Jerusalem, and military orders were found that maintained it for almost a hundred years.
However, during the following Crusades, kings played a progressively decreasing role, sometimes even opposing the pontifical rule. Italian businessmen financed the unsuccessful expeditions led by Saint Bernard of Clairvaux, and later Richard Lionheart together with Frederick Barbarossa.
The 4th Crusade's financial problems
The Pope Innocent III tried to change this situation with the preaching of a 4th Crusade. While carefully avoiding the kings to assume its rule, he planeed a very organised attack into Egypt, the heart of Saladdin's empire. He hired the Venetians for the transport, logistics and reinforcement of troops, and designed the Italian Boniface of Montferrat, descendant of crusaders, as the army leader. In 1202, more than 30,000 crusaders, mostly French, promised to be ready to set sail to Cairo, something that however never happened.
Only a third of the promised soldiers appeared in Venice, and with her little more than half of the silver marks needed to pay. As the Venetians were demanding the payment for their accomplished building of the vessels, a mutual agreement had to be reached. Fainally, the doge Enrico Dandolo, a skillful diplomat and specially a very practical man, managed to attract the Crusade towards his own interests.
Despite the Pope's express ban to the crusaders to "cause atrocious acts against other Christian neighbors", the Venetians demanded as a payment to capture the city of Zara, rebel to Venice and protected by the king Emeric of Hungary and Croatia, who had previously supported the Crusade. Some of the crusaders, disappointed, returned home, while most of them faced a menace of excommunication after taking the city.
Meanwhile, the theoretical leader Boniface, aiming to take initiative back and save the Crusade, met Alexius Angelicus, brother-in-law of his cousin, and son of the Byzantine emperor Isaac, ovethrown some years before by his uncle -also Alexius- who now held the crown of Constantinople. Alexius promised financing and reinforcements for the expedition if they helped him to have the throne back. Most of the crusaders accepted, and specially did the Venetians, as the usurper had expelled their merchants when he came to power.
The city fell when the emperor quickly fleed, and Alexius IV was crowned in Constantinople. However, he soon found huge problems to find the gold and silver promised to his partners, despite melting large amounts of valuable objects in the city. This attack to the possessions of the population, together with the growing hate towards foreigners who occupied their city, caused many fights between Greeks and crusades in the streets and in the court.
In January 1204, a courtesan leader of the anti-Latin movement eventually strangled the emperor -the favorite manner to overthrown in Byzantium- and proclaimed himself emperor as Alexius V. The first thing he did was terminate the contract with the crusaders and expel them from the city. These assaulted it, but were driven back due to the fierce resistance of the Greek population.
The Christians' demoralization nearly made them retreat. However, the clergy that accompanied them used an effective speech, ignoring the continuous orders from the Pope Innocent to cancel that attack against Christians: this action was not God's punishment for their sins, but a test to their spirits. It was the Greeks, murderers and treacherous for killing their patron, and literally "worse than Jews", who deserved to die. The result of this was effectively the conquest of the city some days later, but followed from a sack that is considered as the History's most violent and humiliating one.
During three days, and despite the Venetians trying to keep calm, French knights went on killing the population, destroying art pieces, burned books, murdered priests and raped nuns. The Byzantine historian Niketas Choniates tells in his chronicle of the sack of Constantinople that the crusaders spent several days getting drunk in the throne room in the imperial palace, while a prostitute occupied the throne. The Pope Innocent, in his 1205 letters, writes about the shame he feels because of the crusaders' actions, and the ultimate schism between the Roman and Orthodox Churches takes place: "How could the Greek Church get back (...) to an ecclesiastic union and devotion to the Apostolic See, when it has been seen in the Latins only an example of perdition and darkness, and now, with reason, detests them more than dogs?"
After the end
The creation of the Eastern Latin Empire, divided in a series of states belonging to Venetian and French lords, was saluted as a decisive element to the success of future Crusades. Actually, treasons, banishments and murders followed one another during the half century the empire lasted, and the Latin emperor showed always unable to obtain the support of the Greek population, and resist the attacks from Turks and Bulgarians. It is, in fact, from a Greek territory, Nicaea, that Michael Paleologos eventually assures the reconquest of Constantinople in 1261 and restores the Byzantine Empire. However, the always great Eastern city never recovered, and the Empire became a degeneration of its ancient meaning until it fell in Turkish hands.
From the 13th Century, the idea of Crusade decays, as something old-fashioned. It is often used as an excuse to make war against heretics or enemies of Rome, so that its moral power finally runs out in Europe except in Cyprus, seat of the knights of Jerusalem, and Rhodes, base of the Hospitaller, who will still dream obsessed with the idea for two centuries.