Charlemagne worked very closely with the Papacy, and both believed the expanding Muslim influence to be a threat to Christendom. In the Mid-Eighth Century, Charlemagne began a war with the Muslims under the Umayyad Caliphate to stop their expansion.

Genghis Khan's empire stretched from China to Western Asia but his advance into Africa was arrested by Mamluks, a group of slaves who freed themselves and then immediately fought off the Mongol army.

The Red Guards were young Maoists during the Cultural Revolution in China, they existed hundreds of years after Genghis Khan's empire had already collapsed.

The Vietcong were Communist Vietnamese in the 20th century who fought against the United States, they existed hundreds of years after the Mongol empire had already collapsed.

The Confederates were a group of southern planters and soldiers who attempted to break away from the American union in order to protect their slavery based economy.

The Boxers were 19th century anti-Western fighters, they existed long after the Mongol empire had already collapsed.

The Hundred Years’ War, which lasted, off and on, from 1337 to 1453, and was fought between England and France, was caused by a perfect storm of motivations. Taken together, various social, economic, and political factors conspired to push these two nations ever deeper into the throes of military and nationalistic conflict. One of the main causes was a long history of disputed ownership of the territory of Flanders – a prosperous center of cloth manufacturing, France technically owned Flanders, but many of the territory’s citizens and funds were far more loyal to England, which provided the territory with the wool it needed for its cloth industry. The English King Edward III also administered several former French pieces of land – but these lands were still nominally owned by the French crown, which had loaned the territories to England since the Norman Conquest. By the time of the outbreak of the Hundred Years’ War, neither nation was content with this system of land loaning, because each side believed that it deserved sole control over these territories. Relations were worsened when Edward III declared that he was the rightful heir to the French King Charles IV, who died in 1328 without a male heir. Enraged by the English king’s pretensions, the French nobility selected Philip VI as their new ruler, which outraged Edward III in turn. The long tradition of hatred between these two nations, nurtured within both English and French societies for centuries, at last came to a violent head.

While France wielded several advantages over England during the Hundred Years’ War, the strength of the French military cannot be counted as one of them. In fact, when it came to overall strength, the English military was by far more superior, especially in terms of both their level of training and their weaponry (English archers were known for their keen use of the treacherous longbow). By contrast, the French army, although larger – which reflected the overall greater size of the French population – was not nearly as well trained as their English counterparts. However, the French government was much richer than their English foes, which helped them to be able to procure more replacements (of both men and weapons) after every English victory, while the English army had a more difficult time finding replacement weapons and fighting men. Perhaps most crucially, France possessed the defensive advantage – because most of the fighting ended up occurring on French lands, the French soldiers were automatically able to benefit from their knowledge of the terrain and the support of the local peasant population. The English army, meanwhile, was forced to navigate across unfamiliar territory, coming up against obstacles put in their way by both nature and the local populace. Lastly, French morale received a substantial boost from the inspiration presence, speeches, and military engagement of the famous Joan of Arc. The so-called Maid of Orleans, with her courageous fighting spirit, encouraged the French people to fight onward, even after devastating defeats.

In 1233, Genghis Khan, with a massive force of highly skilled Mongol warriors behind him, attacked Russia. By this time, the Mongols had invaded and conquered various parts of China and the Middle East, and Moscow found itself hard-pressed to withstand the ruthlessly targeted invasion of its territory, as Genghis Khan gained control of more and more swathes of Russian land. With the final fall of Russia to Mongol forces in 1240, the country came under firm Mongol control and would remain a part of the Mongol Empire for almost three centuries (until Ivan the Great’s liberation of his people in 1480). As a Mongol-controlled state, Russia adopted a curious mixture of Christian, Mongol, and Islamic practices, although the Russian people were allowed to preserve a great deal of their religious and political policies. The Mongols moved the center of Russian political, social, economic, and cultural primacy from Moscow to Kiev; the city would remain a potent force within Russian life for centuries to come.

Prior to the invention of the cannon in the fourteenth century, the most useful weapon a lord or a king could have was a castle. Castles were built of stone and could withstand constant barrage from trebuchets and catapults provided they were sufficiently manned; however, the invention and subsequent improvement of the cannon gradually rendered castles obsolete as the additional firepower of a cannon could blast right through the stone walls of a castle. This changed not only military life, but also social, economic, and political life in Europe as the feudal system, predicated in many ways on the protection offered by the lord's castle or stronghold, became gradually obsolete.

The Battle of Talas was fought between the Arab Abbasid Caliphate and the Chinese Tang Dynasty in 751 CE. Prior to the battle, Chinese forces had been spreading rapidly westward and facing little opposition; however, at the Battle of Talas, they were defeated by the Arab forces, and Chinese expansion was halted for several centuries. The battle is considered important for transferring control over the “Silk Road” from Chinese to Arab hands and for turning back the massive forces of the Tang Dynasty. Also, it is sometimes said that Arabs learned the art of paper making from the Chinese prisoners they captured in the battle, thus spreading paper-making technology to the Middle East and eventually Europe.

In 1096 C.E., Pope Urban launched the First Crusade in order to take back control of Jerusalem from the Seljuk Turks. The many crusades that followed all professed a desire for Christian control of the Holy Land, a place that both Christians and Muslims saw as an essential part of their religious identity. Although a Latin Empire was established in Constantinople during the Fourth Crusade, this development ultimately distracted from the crusaders' goals and deepened the schism between the two Christian churches. While the most positive result of the Crusades was arguably the European rediscovery of ancient ideas, this development was also unintended.

Temujin is the given name of the warrior ruler Genghis Khan. Genghis Khan united the Mongol tribes in the twelfth century under his rule and soon led his horde on a series of conquests across Eurasia. In the generations immediately following his death the Mongols conquered the largest land empire ever seen in human history - stretching from China all the way to the gates of Vienna, and including much of northern India and the Middle East. 

Pope Urban II was Pope from 1088 to 1099. He is most frequently remembered for initiating the First Crusade, which led to the temporary conquest of Jerusalem by the forces of Christendom and led to centuries of conflict between Christian Europe and the Islamic world.