The Mongol Empire is the largest land empire the world has ever seen. At its height, it stretched from Siberia down to the Middle East and from China to Eastern Europe. The Mongols committed some of the worst atrocities in human history to conquer their empire, but once their empire was conquered, it facilitated trade in a way unseen previously in human history. The fact that all territory between China and the Mediterranean was effectively governed by one administration ensured that trade could flow freely and people could move safely as never before.

Genghis Khan conquered the largest empire the world has ever seen. His empire stretched from China all the way to Central Europe and from Northern Russia down to the Middle East. It was the first incidence in human history where the massive stretch of land between Asia and Europe could be considered somewhat unified and organized. This connected Europe and Asia into one cohesive trade network for the first time in human history and helped facilitate the exchange of ideas, produce, and disease across the entire landmass.

Meritocracy is the name given to a system in which promotions are made and jobs awarded based on the ability of an individual rather than the status of his or her family. Genghis Khan famously introduced this concept to his Mongolian forces, greatly improving the efficiency of his forces and the loyalty of his men.

Trebuchets are siege weapons that became a popular component of medieval war-making in the twelfth century. A trebuchet is similar in design to a catapult, although significantly more complicated and effective. Trebuchets were eventually phased out in the sixteenth and seventeenth centuries with the advent of gunpowder and cannons.

The invention of gunpowder happened in China sometime around the ninth or tenth century. The China of this time period was a highly innovative society that gave the world many notable inventions, including block printing and compass navigation at sea. Gunpowder spread across Central Asia and the Middle East before arriving in Europe around the thirteenth century.

The Frankish Kingdom arose in the sixth century in an area that comprises most of modern-day France and the Low Countries. It was built on the conquest of Clovis, who converted to Christianity having won a major battle; however, in Frankish culture, the territory of a ruler is divided between his sons, so the Frankish Kingdom continued to fracture and be reformed through conquest for the next few hundred years.

Charlemagne is the most famous and most successful (in terms of military conquests) of all the Frankish kings. At the height of his empire in the year 800 CE, he controlled all of modern-day France, and much of modern-day Spain, Italy, Germany, Austria, and the Low Countries. Because he was a powerful and devout Christian ruler, he was invited to become the first "Emperor of the Romans" in a few hundred years, an invitation he gleefully accepted.

The British Isles were originally held primarily by the Iceni, Gallic, and Celtic people; however, they were conquered by the Roman Empire in 44 BCE. During and after the fall of the Roman Empire, the British Isles were conquered by various Germanic tribes, most notably the Angles, the Saxons, and the Jutes. English people are often called Anglo-Saxon to this day.

Charles Martel was the ruler of the Frankish people in the early eighth century C.E. He is most famous for defending the realms of Christendom from Islamic invasion in 732 C.E. when he won the Battle of Tours. Islamic armies never reached further north than Spain in Western Europe. Without Martel's victory, it is very possible that all of Europe would eventually have been Islamic instead of Christianity, and the whole history of the world would be very different.

Lay investiture is the name given to the common medieval practice whereby the Holy Roman Emperor, or another secular ruler, would appoint church officials without the consent of the Papacy. Gregory VII saw this as a challenge to his rule and banned the practice. He also subsequently excommunicated Emperor Henry IV when he ignored this rule.