European knights flooded the Holy Land during the 11th century as Crusaders began history's most famous holy war.
European knights flooded the Holy Land during the 11th century as Crusaders began history's most famous holy war.

If there is a single concurrent theme that unites the entire Medieval era -- the approximate millennium between the fall of the Roman Empire and the beginning of the 16th century in the Western World -- it is religious conflict. The era was marred by pagan barbarian incursions and ongoing violence between Christians and Muslims, as well as infighting among sects within the two dominant faiths. Jews, for the entirety of the Medieval period, were targeted and scapegoated by factions within both warring religions.

Early Islamic Conquests

At the time of the Prophet Muhammed's death in 632, nearly a century and a half had passed since the Western Roman Empire fell and the Eastern Roman, or Byzantine Empire, was created. A year later in 633, the first Muslim conquests began as North African tribes united by Islam formed armies and set their sights on the Christian Byzantine Empire, initially taking Egypt and Syria. Ferocious religious conflicts would continue until Constantinople, the most cherished Byzantine city, was conquered by the Ottomans and renamed Istanbul in 1453, more than 800 years later.

Viking Invasions

In the late 8th century, Norse Vikings -- widely considered history's most accomplished and famous seafaring warriors -- began raiding Northern Europe, starting with England, Ireland, Wales and then later reaching modern-day France, Portugal, Spain and Eastern Europe. Vikings were polytheistic and believed that they were divinely inspired to engage in commercial conquest, and that success in battle would be rewarded in the afterlife. Terrified Christian Europe began a campaign of mass militarization that would lead to the culture of knighthood and the rise of the first Christian holy warriors.

The Crusades

In an era trademarked by brutal religious conflict, the Crusades stand in a category of their own. The Crusades were six separate holy wars that took place between 1096-1229, when a series of popes called on Western Christians to come to the aid of their Eastern Byzantine counterparts to ward off increasing Islamic encroachment. Savage battles to reclaim the Holy Land for Christianity led to back-and-forth conquering and re-conquering -- with enormous atrocities committed by both sides -- until Muslim defenders finally drove out the European crusaders and regained control of the modern-day Middle East.

Jewish Pogroms

The charge of deicide -- that Jews and their descendants bear collective, hereditary guilt for the execution of Jesus Christ -- can be traced to the book of Matthew and was a pillar of Catholic dogma until the Vatican II Council of the early 1960s. As religious minorities who accepted the divinity of neither Mohammed nor Jesus, Jews were convenient targets in both Christian and Muslim lands throughout the Middle Ages, but endured particularly consistent and cruel treatment in Catholic Western Europe. Virtually every major upheaval, from the Inquisition to the Crusades to the bubonic plague, came with mass persecution, forced conversion, torture, expulsion and wholesale murder of Jews.