In looking through the events in human world history, it is most interesting when one examines the issue of causation. Take the conquest of the Native Americans by the Spaniards about five hundred years ago. Why did this event come about? One might say that the Spaniards possessed more advanced technology in the form of better weapons such as guns and killer germs that the Indians had never seen before. Riding on exotic animals (to the Native Americans) known as horses, the Spaniards decimated a mighty Native American empire with only a handful of men.
However, the causes given above are only immediate causes, not ultimate causes. One can and should ask the question of what events or circumstances drove these proximate causes? Why did the Spaniards have better technology? A simple analysis might conclude that the event that caused the Spaniards to have the superior technology was the original development of writing. But once again, the same question can be asked. What caused writing to develop in Spain? Why did writing not arise in the Inca empire? This process of analysis and discovery of proximate causes resulting from more ultimate causes forms the basis of Jared Diamond's book - Guns, Germs, and Steel.
In his book, Diamond argues that particular events possess a set of immediate causes that spring up from more ultimate causes. The reason that it was the Spaniards conquering the Native Americans and not the Native Americans going to Spain and capturing Charles I is due to immediate causes that favor the Spaniards. However, it is important to note that the Spanish superiority was not a result of "racist" reasons. Rather, the ultimate causes of the Spanish superiority over the Native Americans can be traced back to certain ultimate factors such as the alignment of the continental axes and the extinction of large mammals in North America tens of thousands years ago.
To Diamond, analyzing history in this way is analogous to the peeling of an onion.