The Hundred Years' War was fought between the Kingdom of France and the Kingdom of England from 1337 until 1453. It is one of the most important and notable conflicts of the Middle Ages and as a result of the conflict strong national identities were formed in each nation and the subsequent theory and idea of 'nationalism' was founded. 

In medieval Europe, the Pope had the authority to declare a crusade. A crusade was a holy war that was meant to advance the cause of Christianity and strengthen the power of the Catholic church. The most famous crusades are those launched against the Muslim kingdoms of the Middle East that were generally intended to recapture Jerusalem and the Holy Land.

Enrico Dandolo ruled over the Italian city-state of Venice at the height of its power and influence. Venice, at the time, was an influential maritime city-state and was immensely wealthy as a result of trade in the Mediterranean. Enrico Dandolo is most notable for calling for the Fourth Crusade.

Beginning in the tenth century, the Abbasid Caliphate experienced a steady decline in power. Throughout the tenth century, they lost territory due to nomadic invaders and the chaos caused by Sunni-Shiite divisions. In the eleventh century, the Abbasid capital, Baghdad, was captured by the Seljuk Turks. Although the Seljuk Turks allowed the caliph to continue ruling in a limited capacity, the Abbasid Caliphate would never again rule with any real authority.

All of these were part of the longterm consequences of the Crusades. The role of knights in the Crusades led to the growth of chivalry as a social code in Europe. Relations between the Islamic and Christian world naturally worsened as a result of two centuries of warfare and massacres. In many ways, we are still feeling the effects of this today; however, there were positive consequences too. The reawakening of classical knowledge, that had for so long been preserved by the Byzantines and the Islamic empires of the Middle East, led to the Renaissance in Europe. The exposure to Middle Eastern technology led to greater technological exchange in Eurasia, which was particularly beneficial to the Europeans.

In the late-eleventh century, at the time of the First Crusade, the Islamic world was highly fragmented and resistance was weak and poorly organized. The Abbasid Caliphate was very weak at this time and incapable of coordinating resistance. However, over time the Islamic resistance grew much stronger and by the time of the Third Crusade (1189 - 1212), they were able to hold off the Christian advance on Jerusalem.

The stated goal of the crusades was reclaiming Jerusalem from Muslim armies and spreading the "true faith" of Christianity. In addition to the religious goals, the crusades provided significant opportunities for political gain. In the middle ages, land was power and a war meant the opportunity to gain land. Noblemen from across western Europe flocked to the Middle East in an effort to gain the glory that would lead to greater power abroad that would translate back to their homelands. The Europeans saw anyone who was not of the Christian faith as a pagan or a heretic who was living in sin, they had little to no regard for the inhabitants of the cities they were fighting for.

While the crusades were a constant back and forth between European and Islamic forces, the crusaders were unable to ever permanently drive Islamic armies out of Jerusalem and other Holy Lands. 

Islam emerged in Arabia in the early seventh century and practically exploded onto the world stage. Within a century of the death of the Prophet Muhammad, Islamic territory stretched from Spain, all the way across North Africa and the Middle East, to as far east as modern-day Pakistan.

The First Crusade was waged from 1096-1099 and ended with the brutally violent conquest of Jerusalem by the Crusaders. The Crusaders established a series of small Crusader States on the Mediterranean coast of the Middle East, which they would rule with varying degrees of control for the next two centuries.