Let's finish what we started a few days ago. The ultimate answer on why Pizarro conquered the Incas, on why the Europeans formed the strongest civilizations (rather than the Americans or the Africans) can be clearly seen on any world map. Everyone has noticed it yet it is not easy to relate the picture to human history. It has to do with the continent orientation.
From all continents in the world, Eurasia, America and Africa favored civilizations to grow because the do not require ships - a technology available later in human history. From these 3, Africa and America have a North-South orientation of their axis, while Eurasia in the only one that has a East-West axis orientation. Why does this matter?
Diamond has a very elegant example:
Imagine a Canadian farmer foolish enough to plant a race of corn adapted to growing farther south, in Mexico. The unfortunate corn plant, following its Mexico-adapted genetic program, would prepare to thrust up its shoots in March, only to find itself still buried under 10 feet of snow.
The East-West axis orientation allows for faster and more efficient spread of plants and animals - because all the lands will have the same latitude and more or less the same climate, same rainfall, same year-long cycle of plant growth. How could the Egyptian civilization evolve beyond Sahara, past the tropical forests? How could plants from Eastern US (where they were first domesticated) could ever reach past the Texas deserts into Mexico and meso-america? Yet it's no big deal for Babylonian and Sumerian plants to get to the greeks, the romans and further inside Europe.
In the next step, plant domestication allowed food production: dense populations, complex societies and hence political organization and technology. Animal domestication provided necessary nutrition and goods, plus ensured the growth of germs (all germs come originally from animals) that decimated more than half of the Native American populations (who had no animals apart from the dog -> no germs developed).
Why Europeans and not the Chinese? Because the european terrain is such that encourages small independent tribes to form - which will eventually collide with eachother and that forced them to develop more technology and weapons and be more aggressive. The China terrain on the other hand favors people to be together and hence form a peaceful society. If you need to proof, just wonder why China is one big country while europe consists of several small pieces-countries.
Diamond provides a very detailed history of the continents. From 0, 13,000 years ago, to where we are now. An alien civilization wise enough could have watched our planet at 11,000BC and predict that Eurasian civilizations would have a head start (according to such arguments) and colonize the world - something that eventually happened. The question is now, can we use such arguments to predict the future from where we are now?
