A commonly cited answer is found in the title of Jared Diamond’s development classic, Guns, Germs and Steel: A Short History of Everybody for the Last 13,000 Years. Francisco Pizarro defeated Atahualpa because he had guns, germs and steel, and the Incans didn’t. But this just pushes the question back one step: Why did the Spanish, rather than the Incans, end up with guns, germs and steel? Are Spanish people genetically superior? Is Spanish thought more amenable to innovation and technological advancement? Are Spaniards more intelligent by nature? More creative? Luckier? Or what?

Everyone reading this will sense that any explanations based on genes, biology, superiority, intelligence or other innate qualities are morally unacceptable. That way lies colonialism, paternalism, racism, eugenics, and all their works. But that is not the same as understanding why those explanations are wrong, and/or which explanations should replace them. Without such an alternative account, there is always the risk that some kind of racial superiority—whether the soft variety (our ideas are better than yours) or the hard variety (our stock is better than yours)—will sneak in through the back door.

Diamond’s answer, in a word, is geography. Some societies developed faster than others because of maps, not chaps. There has, in the last couple of decades, been a flurry of books making this argument in all sorts of ways; Ian Morris’s Why the West Rules—For Now is excellent (until it gets into weird transhumanist speculation at the end), Tim Marshall’s Prisoners of Geography applies the same kind of logic to contemporary politics, and so on. But Diamond’s stands apart, both for the superb writing and for the clarity of the argument. Here, in the form of a wince-inducingly crass list, are five of the reasons he gives.

1. Cereals. Native to East Asia, and particularly to the area between the Yellow and Yangtze rivers (where the Chinese population core developed), is rice. Native to West Asia, and particularly to the Fertile Crescent (where the Ancient Near Eastern civilisations developed), are barley, two types of wheat, and three types of pulses. These cereal crops are more easily grown and stored, and provide more calories and protein, than the cereals which predominate elsewhere (maize, sorghum, millet, and so on), and obviously far more than the sorts of plants on which hunter-gatherers have to survive (fruit, nuts, tubers). That gives the people who live in such areas a significant developmental advantage.

2. Large mammals. If you were looking for animals to domesticate—mammals which can be bred in captivity and which are large enough and tame enough to provide you with milk, meat, clothing and/or muscle power—you would want to live in Eurasia. SubSaharan Africa and Australia have plenty of species which are great for tourism but hopeless for farming (would you want to milk an elephant? ride a kangaroo? yoke a rhino?) The only domesticable large mammal in the Americas is the llama or alpaca, and they cannot be trained for war or for ploughing. Eurasia, by contrast, has cows, pigs, donkeys, sheep, goats, camels and horses, which between them can be used for transport, farming, milk, cheese, hides, meat, war and so on. This gives another significant advantage.

3. Continental shape. Not only did Eurasia have more species of cultivable plants and domesticable mammals, it is also shaped in such a way as to facilitate the spread of crops and animals, and therefore humans, and therefore trade, ideas, technology and so on. Eurasia’s axis runs sideways, from East to West, so plants and animals which are native to one part of the continent will often be able to thrive in another part (because a change of latitude does not mean a dramatic change of landscape or climate); wheat and horses could spread across to Portugal or Korea. But Africa and America have axes which run longways, from North to South, which presents far greater obstacles to the spread of agriculture. Potatoes did not reach North America from South America until Europeans had colonised both, and llamas never did.

4. Division of labour. As food production goes up, so does the density of population, and this allows some people in a society to stop looking for food (whether by hunting and gathering, or by farming) and develop writing, religion, social hierarchy, philosophy, bureaucracy, trade, military power, exploration, and so on, all of which are important for social development. This is a big part of how the Maoris conquered Polynesia, and Pizarro defeated Atahualpa.

5. Diseases. Living in close proximity to domestic mammals, and many other human beings, spreads disease. Which is unfortunate for the people who die, but for the people who don’t, and develop immunity, it turns out to be a significant developmental advantage, the most dramatic demonstration of which is the European invasion of the Americas (where European diseases killed millions of Native Americans, but the reverse did not happen on anything like the same scale).

Taken together, these reasons (along with a whole host of others) provide a compelling explanation of why some continents developed faster than others, and Diamond concludes his book with six case studies that show how this worked itself out in practice. If the book has a flaw, it is the risk of reductionism; in responding to an idealist account, in which thoughts and individuals are the primary movers in human history, it risks falling into the opposite trap, namely that of denying any determinative role for human agency. (A more granular reading of history suggests that some ideas, social structures, religions and worldviews are more conducive to human development than others; as such, Diamond’s theory works far better for the differences between continents than for the differences between regions, let alone nations or tribes.) But in fairness, this is not what his book is attempting to do. It is trying to explain why the people who lived in some parts of the world developed faster than the people who lived in others, and in that sense, it has manifestly succeeded.

I am twenty years late to the party on this one (the book won a Pulitzer Prize in 1998, my wife read it at university, and I just read the 20th anniversary edition), so you may already know all this. But if not, this is undoubtedly one of the best books I have read this year, and I highly recommend it. If you’re looking for a polymathic book that explains why the world is as it is, you won’t find many better.