Jared Diamond takes on the ambitious project of explaining why it is that some continents' civilizations could conquer others, and finds the answer in people's ability to form domestic relationships with plant and animal species. To summarize: more "domesticated" (agricultural, harvested) plants leads to sedentary and eventually specialist-producing civilizations that can develop good weapons and other technology (guns, steel). More domesticated animals living closely a non-nomadic human society, in close proximity to humans, means more human diseases when germs come to move between animal and human hosts. That leads to awful plagues but also to germ resistance in the human survivors...germ resistance that other peoples whose immune systems and internal bacteria etc. have not coevolved with the domesticated animals lack. Explorers from disease-resistant populations carry with them germs that can kill off non-resistant populations to devastating effect, often before the conquerers even arrive in large numbers at all. That is the "germs" part of Diamond's equation.But why is it that some civilizations seem to find it easier than others to domesticate plants and animals, and bring their domesticated plants and animals with them to new lands? Diamond argues that it's partly the luck of the geographical draw: some regions simply have more easily "domesticable" plants and animals than others (for more on what makes a plant or animal "domesticable," see the book. Once one has some plants and animals domesticated, though, mobility becomes an issue, especially for the plants. Plants, with life cycles tied closely to length of day and growing season, move much more easily east (or west) than north (or south). Therefore, people living on the huge, east-west oriented landmass of Eurasia can more easily expand their civilizations across the continent than people living in a north-south oriented continent like Africa or South America; the crops they're used to can thrive. Had the east-west continent of North America been peopled earlier, or contained more domesticable species, European explorers would have had a much harder time conquering North America than they did.The above is the merest, grossest sketch of the sorts of arguments Diamond makes. For evidence to support them, he draws on studies in many different areas, as indeed he needs to if he is to support his broad claims.Some reviewers dislike Diamond's arguments because they leave out major personalities and cultural achievements of rulers and churches or other institutions. In my view, these factors operate at a different level than what Diamond is talking about. Such individuals and institutions do come to exert independent influence on their social and material worlds, but what Diamond is saying is that such entities require some basic conditons in order to flower, and Diamond has taken on the job of naming and explaining those necessary conditions.