During the most recent ice age Asia and North America were connected via a land bridge in the Bering Strait. This allowed humans to migrate from Asia to North America and led to human settlement throughout the Americas. The native people of the Americas are all descended from this group of people who crossed the Bering Strait approximately fifteen thousand years ago. When the ice age ended, Asia and North America were no longer connected, thus isolating the Americas from the rest of the world until European colonization in the 1500s.

Mesopotamia is translated as “The land between two rivers.” It is also the cradle of civilization, for it is here that the Neolithic Revolution first took place. The two rivers in question are the Tigris and Euphrates.

Ancient Egypt was geographically isolated from other civilizations. It was protected on all sides by either desert, sea, or mountains. Ancient Mesopotamia on the other hand lacked natural barriers of any kind. It lies in a fertile valley that was under constant threat of invasion. Many historians speculate that this intensity of competition in Mesopotamia contributed a great deal to the innovations made by Mesopotamian societies.

Pastoralism refers to the practice of keeping domesticated animals. During the later Neolithic Revolution many societies were organized around the domestication of animals such as cows, horses, pigs, sheep, goats, buffaloes, and oxen. Pastoral societies most commonly emerged in wide open plains with plenty of flat grassland. This is compared to agricultural societies which would most likely have emerged in valleys and in the fertile floodplains.

The Old Kingdom of Ancient Egypt was geographically isolated from other human civilizations. Protected by inhospitable deserts, the Mediterranean Sea, and several mountain ranges the ancient Egyptians never developed much of a military culture and were fairly easily conquered by the first militaristic civilization they encountered - the Hyksos.

Llamas and alpacas are two species of camel that are native to South America. Unlike their cousins in Arabia and Central Asia, llamas and alpacas are not renowned for their strength or resilience. The lack of a true “workhorse” type animal in South America (an animal like an ox, camel, horse, or buffalo) decelerated the growth of civilization in the continent for several millennia.

During and after the most recent ice age the Bering Strait (which had connected North America to Asia via a land bridge from Alaska) was flooded and the Americas were isolated from the rest of the world. This geographic separation enforced an environmental and cultural isolation which had a profound impact on the development of American society.

The Plague of Justinian was the first ever outbreak of bubonic plague and would continue to spread exploration westward into Europe. 1340 saw an explosion of bubonic plague that would persist for sixty years, killing a third of the population of Europe. This outbreak would become known as the Black Death.

The Plague of Justinian occurred from 541 - 542 CE Like the later Black Death - which devastated the population of Europe in the fourteenth century - the Plague of Justinian was a widespread epidemic caused by the transmission of the Bubonic Plague. Modern historical estimates range from twenty million to fifty million deaths globally. The population of the Byzantine Empire declined dramatically as a result of the plague. It is called the Plague of Justinian because it occurred during his reign (he was himself afflicted, but he survived).

Population growth and state building have long been hindered in Sub-Saharan Africa by obstacles that simply do not exist in other parts of the world. The extreme prevalence of insect-borne diseases like malaria, which humans are extremely vulnerable to, has had a catastrophic impact on Sub-Saharan human history. Furthermore, the climate of Sub-Saharan Africa fluctuates wildly, including prolonged periods of drought, which made agricultural societies all but impossible until fairly recently. Finally, the massive geographic barrier that is the Sahara Desert kept this region isolated from the rest of Afro-Eurasia until the arrival of Arabs and Europeans. This meant that the people living in Sub-Saharan Africa were not exposed to the same diversity of ideas, resources, and innovations as the rest of the world.