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Setting the stage -

At the turn of the second millennium, in medieval Europe, the papal throne was the most powerful position on the continent. All kings and regional leaders answered to the pope, and religious power was synonymous with political power.

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Unity within the Church -

While some infighting between Western European and Eastern European powers had weakened the overall sway of the Catholic Church, relations between the factions were beginning to heal at the start of the 11th century, and the Church as a whole was starting to once again look towards expansion.

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In the hands of the enemy -

By this time, the city of Jerusalem, the most important city in Christianity, Islam, and Judaism, had been under Muslim control for nearly 500 years. Muslim empires had dominated much of the Middle East since the fall of the Roman Empire.

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Alexios I Komnenos -

Alexios I Komnenos, the Byzantine emperor between 1081 and 1118, was the first to call for a unified Catholic movement eastward, when he addressed the Council of Piacenza in 1095. His empire was facing constant attacks from the Seljuk-Turks and requested military support from the Church.

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Pope Urban II -

Pope Urban II, leader of the Catholic world, enthusiastically expressed his support for Alexios’ request. Not only did he support sending a military force to the eastern Byzantine border, but he called on all Western Europeans to engage in an armed march eastward.

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The First Crusade -

Pope Urban II’s rallying cry was heard across the continent, and armies began to take shape and move eastward. Some of the more organized armies, those under the command of noblemen and feudal lords, took time to form, while other grassroots groups materialized almost instantaneously.

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The People’s Crusade -

The first group to set out and reach the Byzantine Empire was a massive group of peasants who are now referred to as the People’s Crusade. They were led by a French priest known as Peter the Hermit (pictured).

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The first battle of the First Crusade -

Peter and his army arrived at the Bosporus Strait, the frontier between the Christian and Muslim worlds, long before the other more qualified and better-equipped armies did. Impatient and emboldened by their feelings of righteousness, they crossed the strait and charged headfirst into the Seljuk Empire. The enemy forces waiting for them wasted no time decimating the peasant forces, and thus the People’s Crusade was no more.

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The four armies progress into Anatolia -

The four principal Christian armies of the First Crusade, led by Raymond of Saint-Gilles, Godfrey of Bouillon, Hugh of Vermandois, and Bohemond of Taranto, had more success infiltrating the Seljuk territory, and by June of 1097 they had conquered the Seljuk capital of Nicaea.

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The fall of Jerusalem -

The Crusader armies swiftly moved through the rest of Anatolia towards Jerusalem. After a month-long siege of the holy city, Jerusalem fell at the hands of the Crusaders in July 1099, and the First Crusade ended in a terrible and bloody massacre of the citizens of Jerusalem.

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Formation of the Crusader states -

Once the region had been conquered, the four leaders of the crusader armies formed four spheres of control that came to be known as the Crusader states, including the kingdoms of Jerusalem, Edessa, Antioch, and Tripoli. Once these states were established, large portions of the armies left the region and made their ways back home to Western Europe.

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Beginnings of the Second Crusade -

The Christian forces enjoyed nearly half a century of power in the Holy Land and the surrounding area. Over time, however, the Muslim-Turks began making small victories in their own holy conquest to retake Jerusalem.

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The loss of Edessa -

In 1144, under the command of Seljuk general Zangi, Muslim-Turk forces captured the Kingdom of Edessa, officially breaching the territory of the Crusader states. Panic broke out amongst the Christian leadership when news of this loss reached the West, and a second crusade was organized in 1147.

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Leaders of the Second Crusade -

Two kings led the Second Crusade: King Louis VII of France (pictured), and King Conrad III of Germany. They swiftly moved their armies eastward in hopes of putting a quick end to the Muslim retaking of the Holy Land.

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Battle of Dorylaeum -

Thinking that the second conquest of the Middle East would be as easy as the first, the two European kings came severely underprepared, and their armies were decimated during their first clash with the Seljuk forces at the city of Dorylaeum.

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Defeat at Damascus -

After their defeat at Dorylaeum, the royal armies retreated and regrouped in Jerusalem, and set out once more with a group of 50,000 soldiers, this time towards Damascus, in modern-day Syria.

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Defeat at Damascus -

Unfortunately for Europe and the Church, the kings’ armies were sorely defeated at Damascus as well, in 1149. The Muslim-Turk armies wiped out the last of the Crusaders, and the Second Crusade ended with no sign of the shift of power in the Holy Land that the Europeans wanted.

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A small but important victory -

The only gain made by Europe during the Second Crusade was on the smaller southwestern front, where the Muslim Moors had taken control over parts of the Iberian Peninsula. In 1147, after a four-month-long siege, English and Portuguese forces gained control over the city of Lisbon, which would later become the capital of the Kingdom of Portugal.

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Buildup to the Third Crusade -

Throughout the Second Crusade and the decades that followed, the Christian Crusader forces were able to keep control of the remaining three Crusader states, and kept themselves busy attempting to conquer Egypt.

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Muslim forces retake Jerusalem -

The leader of the sultanate in Egypt, Sultan Saladin, responded to this aggression in 1187 by plowing through the Crusader forces all the way to the city of Jerusalem, held by the Church’s forces since the First Crusade, where he ousted the Christian leadership and placed the holy city back under Muslim control.

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The Kings' Crusade -

This massive loss sparked the Third Crusade, also known as the Kings' Crusade, as it was led by three of the major rulers of Europe: King Philip II of France, King Richard I of England (pictured), and the elderly German Emperor Frederick Barbarossa, who wouldn’t survive the trek eastward.

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King Richard’s victories -

King Richard I’s army defeated Saladin’s forces during the Battle of Arsuf, and regained a large portion of the area surrounding Jerusalem, although he didn’t feel he had the forces to take the city itself.

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Treaty of Jaffa -

In 1192, Richard and Saladin put an end to the Third Crusade by signing the Treaty of Jaffa, which restored the Christian Kingdom of Jerusalem while still leaving the city itself under Saladin’s control, and granting Christian civilians safe passage in and out of the city for religious pilgrimages.

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The Fourth Crusade -

Predictably, the Treaty of Jaffa didn’t remain an acceptable compromise for the Church for very long. In 1202, Pope Innocent III called for a fourth Crusader army to head east and retake Jerusalem in the name of Christianity.

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A change of plans -

As the Fourth Crusade moved eastward, they detoured towards the Byzantine capital of Constantinople after making a deal with Prince Alexios Angelos that stipulated that once the Crusaders put an end to the reign of Alexios’ uncle, Alexius III, allowing Alexios to step in as emperor, Alexios would then provide military and financial support for the Crusaders’ cause.

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The siege of Constantinople -

The resulting siege and sacking of Constantinople that took place in 1203 led to the fall of what was at the time the most glorious and sophisticated metropolis in the Christian world, and marked the beginning of the end for the Byzantine Empire.

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The fall of Constantinople -

After Alexios replaced his uncle in the emperor’s throne, he was met with staunch resistance from the rest of the Byzantine ruling class and lower classes. Before he was able to fulfill his promises to the Crusaders, he was strangled in the palace. The Crusaders got their due by sacking the city and setting it ablaze in what’s now known as the “Great Fire,” which destroyed much of the city.

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Abandonment and retreat westward -

By 1203, the original purpose of the Crusades had long been replaced by general greed and lust for power. Any righteous justification for the widespread violence and destruction of the first four Crusades or the desire to retake the holy city of Jerusalem had been forgotten, and the armies returned straight home after the fall of Constantinople.

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The lesser Crusades -

Other minor campaigns in the name of Christianity were made during the rest of the 13th century, including the bloodless Sixth Crusade, during which the Church briefly regained control of Jerusalem through diplomatic means. However, the Fourth Crusade would mark the practical end of the Crusades, and the seemingly endless battle of cultures and kingdoms would manifest itself in other ways.

Sources: (History) (History Today) (Britannica)

See also: The deadliest religious conflicts in history

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