We're uncomfortable about considering history as a science. It's classified as a social science, which is considered not quite scientific.

In fact, everywhere in the world there has been a flux between big and small societies. Big political units are constantly being formed, later to fragment. The individual pieces try to pull apart, and then they join together again. One sees that in Europe: There have been unifications and then dissolutions and reunifications. So in the long run, it's 10,000 steps toward amalgamation offsetting 9,999 steps toward falling apart again. In businesses and industries, I would guess that's also true.

It invites a search for ultimate causes: why were Europeans, rather than Africans or Native Americans, the ones to end up with guns, the nastiest germs, and steel?

One way to explain the complexity and unpredictability of historical systems, despite their ultimate determinacy, is to note that long chains of causation may separate final effects from ultimate causes lying outside the domain of that field of science.

Take air quality in the United States today: It's about 30 percent better than it was 25 years ago, even though there are now more people driving more cars.

[T]he values to which people cling most stubbornly under inappropriate conditions are those values that were previously the source of their greatest triumphs.

Although native Africans domesticated some plants in the Sahel and in Ethiopia and in tropical West Africa, they acquired valuable domestic animals only later, from the north.