Guns, Germs, and Steel, Jared Diamond is arguing that Europe (and, by extension, places where Europeans settled like the United States and Australia) became rich and powerful simply because of geographic luck.  He is arguing that there was nothing about European people or European culture that made them better than other people.

In this book, Diamond sets out to answer “Yali’s Question.”  This question asks why “white people” came to have so much more material wealth and power than other people.  Diamond says that many people have answered this question by saying that Europeans are in some way superior.  Some have argued that Europeans are genetically superior to other people.  Others have argued that the Europeans are not genetically superior but that they do have cultures that are superior in that their cultures make them work harder and make them more likely to accept and embrace progress.  In Guns, Germs, and Steel, Diamond refutes this idea.

In his book, Diamond argues, instead, that the Europeans came to power because they were lucky.  Diamond says that Europeans became powerful because they lived on a landmass where agriculture arose early.  Agriculture, to Diamond, is very important.  It allows people to live together in large groups that do not move around.  Because these groups do not move around, and because they have more than enough to eat, they can have specialists who create technology.  The sooner a group gets agriculture, the longer it has to create the “guns” and “steel” that helped the Europeans become powerful.  Farming communities also create the conditions in which infectious diseases (the “germs” of the title) can arise.

What this means is that whoever got farming first was likely to become powerful.  Diamond then asks why people in Eurasia got farming first.  He concludes that this happened because that landmass was home to more plants and animals that could be easily domesticated.  This was not something that we should give the Europeans credit for.  They did not develop agriculture and civilization because they were better than other people.  Instead, they developed agriculture earlier because they were lucky.  This luck allowed them to get a head start and to, by modern times, dominate the world.  This is the gist of Jared Diamond’s argument in Guns, Germs, and Steel.

Jared Diamond’s thesis in Guns, Germs, and Steel is that the countries of the world that became rich and powerful did so because of geographical luck.  These countries did not become rich and powerful due to racial or cultural reasons.  They did not become rich and powerful because they were better than other countries.  Instead, they were simply lucky in terms of where they happened to be located relative to things like important natural resources.

When Diamond was working as a biologist in New Guinea, a New Guinean man named Yali asked him why whites were so rich and New Guineans were so poor.  Diamond started to think about this question and eventually wrote this book to present his answer.  Diamond wants to refute the idea (held by many people) that European countries became rich and powerful because they were somehow superior to other cultures.  Many people have thought that Europeans were racially superior to other groups and/or that Europeans had a better culture.  Diamond strongly disagrees with this suggestion.

Diamond’s thesis is that geographic luck was what made some countries rich and powerful and others weak and poor.  He says that the countries that became rich and powerful were those that developed agriculture first.  When countries developed agriculture, they were able to make large, complex societies.  In those large, complex societies, they were able to develop technologies that made them powerful.  Their wealth and power stemmed from their early adoption of agriculture.

But why did these countries get agriculture first?  Diamond’s thesis is that they were simply lucky.  These countries happened to be located in places where there were a large number of plant and animal species that could be domesticated.  They were located in places where it was easy for these domesticated species to spread from one society to another.  Because of this luck, they developed agriculture and, thereby, became rich and powerful.

Diamond’s thesis, then, is that geographic luck played the largest role in determining which countries would become rich and powerful and which would remain relatively poor and powerless.

The central argument in Guns, Germs and Steel by Jared Diamond concerns why some cultures have dominated others. Historians, thinkers, and leaders have perennially asked this question, and the usual theories have included "geography," "climate," and sometimes "race." But Diamond looks at evidence of how geographical continuity across similar climates supported superior agriculture and weaponry. Societies that were similar enough in climate worked together over centuries to create a synergy in technological innovation that, when combined with communication and trade, produced superior technology.

At the core of his thesis is the idea that human knowledge has built on itself in steps, but communication between civilizations happened far more efficiently from East to West and in temperate climates. The rise of civilization in the form of agriculture helped some societies, notably Western European ones, rely on wheat as a consistent protein source. Because the temperate climate of Western and Eastern Europe, and to some degree Russia, was consistent, wheat could be traded, and there was a continuity of goods across huge distances, linking disparate cultures. This allowed traders and others to learn from one another and share technologies. Due to the production of a stable crop (wheat, and to a similar degree in the East, rice), there was more leisure time to develop technologies, and the production of wheat helped create large urban centers (cities) where task and job differentiation blossomed.

The technology that allowed Europeans to dominate less "developed" nations, such as South, Central, and North American indigenous nations and Africans, was in weaponry. Steel changed the game, and guns made weapons like spears, knives, and bows virtually useless in battle. South, Central, and North American natives and Africans did not have the same East-West exchange of knowledge (as their continents were oriented more from North to South). The continuum of technology exchange from North to South meant radically different climates, inconsistent food crops, and difficulty with trade over vast distances—all of which kept cultural and information exchange limited in a North to South orientation.

Diamond points out that guns and steel won wars, but of course, the diseases of Western countries also wiped out millions of people around the world.

Diamond summarizes his thesis in this way:

History followed different courses for different peoples because of differences between peoples' environments, not because of biological differences among peoples themselves.

More specifically, some societies centered in Europe developed the powerful military technologies, diseases, and other factors—"guns, germs, and steel"—that allowed them to dominate other societies without these things. Diamond is arguing that the factors that enabled them to develop these things before others was not traceable to genetic or cultural factors that are used to justify racism. Rather, they were the result of geographic accidents. Some places had more propitious climates, soils, domesticable flora and fauna, and other factors that facilitated the development of settled agriculture. Naturally, stratified societies, technology, and diseases flourished in these societies first, giving them a head start over peoples around the world. There was nothing inherently "better," more competent, or superior about Eurasian peoples; their geographic surroundings were simply well suited to the things that lead to the development of the factors promoting conquest. Diamond's thesis is intended to overturn long-held beliefs about European superiority in particular.

In Guns, Germs, and Steel, Jared Diamond’s thesis is that environmental factors, and not factors like race or culture, determine whether certain societies have become rich and powerful.

Diamond writes this book because he has long been interested in the question of why some societies are so much richer and more powerful than others.  He started thinking about this question when a man in New Guinea asked him why white people were so much richer than people from New Guinea.  Diamond wrote Guns, Germs, and Steel as a way to answer that man’s question.

Many people have tended to think that race or culture caused the differences between various societies’ degrees of wealth and power.  Over history, many people have argued that white people are simply superior to non-white people.  More recently, we have seen people argue that whites are not biologically superior, but that their culture is more adapted to gaining wealth and power than other cultures are.  These types of arguments essentially say that some societies grew richer and more powerful simply because they were in some way better than the poorer and weaker societies.

Diamond’s thesis rejects this.  He argues that some societies got rich simply because they were lucky in terms of where they arose.  He particularly argues that societies got rich if they arose in areas that had many plants and large animals that could be domesticated.  These societies were the first to get agriculture.  This allowed them to build larger and more complex societies.  Because they did so, they were also the first to get technology.  Finally, they became home to infectious diseases to which they developed some immunity (while people in places like the Americas did not).  Their technology, their germs, and their organized societies allowed them to become rich and powerful.

In this book, then, Diamond’s thesis is that the societies that became rich only did so because of geographical luck, not because they were in any way superior to others.

Guns, Germs, and Steel by Jared Diamond begins with a personal anecdote. Diamond is an American scientist with degrees in anthropology and biology who is very interested in how geography and ecology interact with human culture. When on a research trip to Papua New Guinea to study birds, he becomes acquainted with Yali, an important local figure who had served as a soldier and politician and was a follower of the traditional "cargo cults," a religion which is grounded in a notion that a return to traditional moral and cultural behavior will result in a quasi-miraculous appearance of "cargo" or material wealth. Yali asked Diamond:

Why is it that you white people developed so much cargo. . . but we black people had little cargo of our own?

The book is an attempt to answer this question. Diamond argues that the people he has met in his travels are just as intelligent and hardworking as Europeans and that the differences in technology and prosperity are due to geological and ecological ultimate causes, rather than racial or cultural characteristics. 

In this book, Diamond is trying to answer “Yali’s Question.”  Yali was a native of Papua New Guinea who became friendly with Diamond.  At one point, Yali asked Diamond

Why is it that you white people developed so much cargo and brought it to New Guinea, but we black people had little cargo of our own?

When Yali talked about “cargo” he meant material goods.  He was asking why the white people had so much technology and so many material goods while Yali’s own people did not.  This is the basis of the question that Diamond is trying to answer.

The more expanded version of the question is “why were Europeans so much more powerful than other people in the world by the 18th or 19th century?”  Diamond says that people tend to argue that this was because Europeans were racially or culturally better than other kinds of people.  However, Diamond disagrees.  His main thesis in this book is that Europeans came to be richer and more powerful simply because of luck.  They were lucky in terms of their geography and that luck allowed them to become dominant.

Diamond begins his book by describing a question posed to him long ago by Yali, a New Guinea politician he met while doing field work in that country. The question that he asked, according to Diamond, was:

Why is it that you white people developed so much cargo [i.e. goods and technology] and brought it to New Guinea, but we black people had little cargo of our own?

Yali's question is central to Diamond's book. Put another way, he wants to explore how it was that societies around the world developed technology and other aspects of civilization ("guns, germs, and steel") that made it posible for them to dominate other societies. Why did, as he asks later in the book, Pizarro arrive to conquer the Inca and not the other way around? Diamond's main goal is to show that these inequalities developed primarily due to geographic variations that made certain regions more suitable for agriculture than others. It was not, in other words, cultural or, more insidiously, racial superiority that allowed Europeans to dominate the world for so long.

Source: Diamond, Guns, Germs, and Steel, 14.

Diamond’s book is meant to answer a simple question put to him by a politician from Papua New Guinea: given than Europeans and New Guineans are equally smart, why is it that Europeans have so much more stuff? Diamond’s answer avoids the commonplace assertions about culture or race (for instance, that science did not rise in China because Confucianism did not value scientific inquiry) and instead focuses on geography and environment as determining factors.

For Diamond, the rise of technologically sophisticated civilizations in Eurasia can be traced to conditions that made the evolution of agriculture possible—factors such as climate and the availability of native plants that could be domesticated. Agriculture made possible the development of cities, and urbanization in turn affected the genetic make up of the people that lived in the cities—making them more resistant to disease, for example. 

Guns, Germs, and Steel by Jared Diamond attempts to answer Yali's question about why Europeans have so much "cargo" (material wealth and technology) and Papua New Guineans so little. Diamond notes that people from many different regions and cultures are equally intelligent and work equally hard, making this disparity puzzling.

In his book, Diamond argues that there are geographic and environmental factors that led to to variation in wealth and technological development. Among the main factors were those that affected the agricultural transition. Regions with domesticable plants and animals and appropriate rainfall and soils can generate surplus food by farming, leading to specialization of labor, which is an essential precondition for development of advanced technology. This meant that when Europeans encountered other cultures, their more advanced military technology led to conquest. He also argues that the resistance to epidemic diseases resulting from early urbanization also was a major factor in colonialism, as European diseases decimated many indigenous populations.

The main point of this book is that geography, and not things like race or culture, is the main factor that determines which societies have become powerful and have not.  In support of this main point, there are some other major points.  They include:

• Societies are powerful if they have "guns, germs, and steel."
• Societies get "guns, germs, and steel" only if they can become large, agricultural societies.
• Agriculture can develop in some areas and not in others.  
• Geographical factors (like the availability of plants and animals that can be domesticated), rather than race or culture, determine which areas become agricultural and which do not.

In this way, the less important points build up to a proof (in Diamond's mind) of the main point of the book.

Diamond's overall argument is framed as a response to what he identifies in the Prologue as "Yali's question." Yali, a man from New Guinea, posed his question to Diamond when the author was visiting that country on a research excursion. The question was, essentially, why white people had more "cargo," by which he meant material goods and technology, than people like himself. Diamond could not answer the question at the time, but it formed the basis for Guns, Germs, and Steel. In Diamonds's own words, his thesis is this:

History followed different courses for different peoples because of differences between peoples' environments, not because of biological differences between peoples themselves.

As he explains, what he means by this is that European people were able to develop the technology, culture, and diseases (the "guns, germs, and steel") that enabled them to dominate the world for much of its history not because of anything supposedly "superior" about them. Rather, as he shows throughout the book, it is because Eurasia was more suitable for the development of agriculture, and the complex civilizations that it facilitated, than elsewhere. It was due to unique geographic features that Europeans went on to colonize and conquer peoples around the world.

Diamond's overall argument in this book is that some societies come to dominate others because of geographical luck.  The book is meant as an answer to Yali's question.  It is meant to explain why some societies became powerful and others did not.  Some people have argued that this is because of racial characteristics or cultural characteristics of the various societies.  But Diamond does not believe this.  In the book, he argues that the societies that became powerful were simply lucky.  They arose in places where farming was more likely to arise and to spread.  This allowed them to form civilizations, which in turn gave them the technology, the political organization, and even the diseases that helped them dominate the other peoples of the world.

The general theme of Guns, Germs, and Steel is human development.  Diamond is interested in the different levels of development in different societies.  In other words, he wants to know why some societies became so much more wealthy and powerful than others.  Diamond’s overall message is that these differences are caused by geographic factors, not by any factors that are innate to the people or cultures of the various societies.

In our world today, countries populated by people of European descent are, on average, stronger and richer than others.  This was even more true a few decades ago when Diamond started to think about the issues that he explores in this book.  Many people have attributed this difference to inherent qualities of the people and cultures involved.  They have said that Europeans dominate because they are genetically superior or because their culture is more conducive to progress.  Diamond disagrees.  Diamond says that Europeans came to dominate through geographical luck.  He says that Eurasia was more suited to agriculture than any other region in the world.  Therefore, agriculture arose there first and spread more easily in Eurasia than elsewhere.  Because this area got agriculture first, it also developed civilization and technology first.  It had a longer time in which its civilizations could grow and develop.  Therefore, by modern times, Europeans and their descendants had come to dominate the world.

Diamond argues, then, that differences in human development around the world are caused by geographical luck rather than by any factors that make the people of one society superior to the people of another.

Diamond frames his book as a response to a question posed to him by a New Guinean man named Yali during a research visit there. Yali wanted to known why it was that white people had so much "cargo" (i.e., material goods) and people like him had so little. This question cuts to the heart of world history as Diamond sees it, and his thesis is essentially an answer to it. His basic argument is as follows, in his own words:

History followed different courses for different peoples because of differences among people's environments, not because of biological differences between peoples themselves (25).

It is not really genetic or cultural factors that facilitated the growth of modern civilizations in Eurasia, but accidents of geography. Certain regions were more conducive to the development of agriculture, which contributed to the development of complex societies capable of creating the "guns, germs, and steel" that gave them a sort of competitive advantage over other peoples. The transition of societies from hunter-gatherer to agriculturalist had far more to do with the availability of domesticable animals and plants, for example, than any cultural factors. Especially important was the orientation of some continents (like Europe) along an east-west axis instead of a north-south one. This meant that there were more areas with similar climates through which domesticated crops might spread. So Diamond's argument is that factors like these played a decisive role in shaping human history.

Jared Diamond is a professor at UCLA.  He has written several books about the history of mankind.  He has written "Guns, Germs, and Steel" in an attempt to enlighten society on why we have developed in the manner that we have.  Why is the USA so powerful?  Why is it when the African continent had such a head start that the Eurasia nations lead the world in technology?  Diamond attempts to explain 13,000 years of history in 471 pages. His thesis is stated on page 25 of the chapter entitled "Yali's Question";

"History followed different courses for different peoples because of differences among peoples' environments, not because of biological differences among poples themselves." 

The thesis that Diamond is trying to prove in this book is that geography determined the major trends in human history.  He is trying to show that it is geographical luck, and not racial or cultural superiority, that led to the dominance of Europeans over other societies of the world.  Diamond starts with "Yali's question," in which he is asked why white people are so much richer and more powerful than New Guineans.  In this book, he attempts to show that geography causes these differences.  On p. 25 in the paperback edition of the book, Diamond provides a succinct statement of this thesis when he says that some people dominate and others are dominated

...because of differences among peoples' environments, not because of biological differences among peoples themselves.