Jared Diamond’s Guns, Germs, Steel offers the most compelling explanation. Diamond focuses on the importance of geography. Diamond argues that there are surprisingly few domesticable animals and crops. Regions of the world with domesticable animals and crops developed agriculture. And agriculture was the key towards getting guns, germs and steel. And these are the keys to the success of the Europeans.

The uneven distribution of domesticable plants and animals led some parts of the world, Eurasia in particular to develop agriculture.

Today two cereals, wheat and rice, account for 41% of all total calories consumed in the world.
Wheat is native to just the fertile crescent, around modern Turkey and Iraq.
Rice from China.
The major cereals are wheat, corn, rice, barley, and sorghum.
4 out 5 of these are from Euroasia (sorghum is from North Africa which is effectively party of EuroAsia? rather than Africa).
The indigeneous versions of wheat, rice, barley and sorghum are very similar to the domesticated versions. Corn is from MesoAmerica? and the wild version is very different. It consequently took much longer to domesticate.
Many plants are surpisingly difficult to domesticate.
Diamond argues that the domesticated plants are evidence of the domesticable plants and that these were not evenly distributed across the globe.

East and West Note:

Agriculture and other ideas also spread faster in Euroasia because it’s major axis is East-West?, along a similar latitude, meaning a similar climate, so crops, animals and ideas could move more easily across Euroasia than through the Americas or Africa where the major axis is North-South?.

Big, domesticated animals are important they provide meat, milk, fertilizer, transport, clothing (e.g. wool and leather), military assault capacity, power (e.g. plowing).There are surprisingly few domesticated animals.

In the world today there are five major cases: sheep, goats, cows, pigs and horses.
Add in some less important cases: Arabian camel, Bactrian camel, Llama and Alpaca, Donkey, Reindeer, Water Buffalo, Yak, Bali cattle, Mithan we have a total of 14.
The wild ancestors of these animals were not spread evenly across the globe.
None of the ancestors to these animals was indigenous to sub-Saharan Africa.
Only the Llama/Alpaca had a wild ancestor indigenous to South or North America.
13 of 14 were indigenous to Euroasia.

Without domesticated animals it’s much harder to develop mass agriculture and from there cities and civilizations.

Farming also leads to getting germs. People with farms can maintain livestock. Livestock give us germs. Many of our diseases come from animals. Measles from pigs. Smallpox and anthrax from cattle. People also started to become sedentary and lived in towns and cities and farming and the development of farming led to higher population growth (especially during the second farming revolution).

Germs are everywhere (including this computer). By getting germs, we force our immune system to work. Those with weak immune systems die and those with stronger immune systems live. The plague wiped out a third of Europe but there is evidence that some of those survivors of the plague have a stronger immune system.

Even with the advantages of guns, steel and horses, conquest of North and South America might have been a close call had it not been for germs.
The major infectious diseases in humans all evolved from diseases of animals:
Smallpox Flu Tuberculosis Malaria Plague Measles Cholera
Europeans lived next door and often in the same barn as the animals and were repeatedly decimated by these diseases but for that very reason they evolved some immunity
Smallpox in S. America where it may have killed 90%, yes 90% of the population.

When the Europeans came to America, the Aztecs and Incans got the diseases Europeans had been exposed to over and over again over hundreds of years. As a result, both societies got wiped out.
The population of the area of Mexico went from 25 million to 1 million within 50 years of the Spanish meeting up with the Aztecs.

Bands, Tribes, Chiefdoms and States
Societies that get ahead thanks to the advantages of good farming will rise up from the level of band to the level of state. As they rise up to a higher level, they will get more complex, larger in numbers and more differentiated in jobs thanks to new technologies that require differing skillsets.

NumbersDozensHundredsThousandsOver 50,000
Ethnicity111More than 1
GovernmentEqualEqualCentralized and Hereditary Centralized
Bureaucracynonenone1 or more levelsMany levels
Monopoly of ForceNoNoYesYes
Conflict ResolutionInformalInformalCentralizedLaws,judges
HierarchyNoNoMain villageCapital
Food ProductionNoNo-yesYes-intensiveIntensive
EconomyReciprocalReciprocalRedistributiveRedistributive Taxes
Control of LandBandClanChiefVarious
StratifiedNoNoYes, by kinYes
Public WorksNoNoYesYes
Widespread LiteracyNoNoNoYes