Diamond’s analysis of Africa’s development attempts to solve two puzzles. Why did the Bantu come to dominate much of sub-Saharan Africa, though not present-day South Africa? And why, if Africa had a head start of millions of years in the evolution of human society over all other regions of the world, did Europeans rapidly and successfully colonize Africa, rather than vice versa? Explain his answers to both of these questions.
The answer to this question can be found in Chapter 19 of Guns, Germs, and Steel. More specifically, it is found in its most concise form in pages 396 through 398 of the paperback edition of the book. There, we are told that climate and environment, along with the crops and domesticable animals that were available to the different groups of people, caused the phenomena that you ask about in this question.
The Bantu were able to dominate most of sub-Saharan Africa because they had the right kinds of crops, animals, and technology. Diamond asserts that all of the domesticable plants in Africa originated north of the equator. This means that none of the people of the more southern parts of Africa had any native domesticable plants. Therefore, they could not farm.
We know from the rest of Guns, Germs, and Steel that farming societies have major advantages over hunter-gatherer societies. This was true of the Bantu. They had larger populations and more complex societies, which gave them an advantage over people like the Khoisan and the Pygmies. They also had crops that would grow in the climate of most of southern Africa. Once they got to the eastern part of Africa (the Great Rift Valley), they acquired more crops as well as cattle and iron. These additions made them essentially invincible. In other words, the Bantu came to dominate this area because they had farming where the native peoples of those areas did not.
So why did the Bantu not colonize the southernmost part of Africa? This is also because of climate and crops. Their crops were adapted for summer rains such as fall in most of sub-Saharan Africa. However, the southernmost part of Africa has a Mediterranean climate with winter rains. Therefore, Bantu crops could not grow there and the Bantu could not dominate.
By contrast, the Europeans were able to dominate this area (and much of the rest of sub-Saharan Africa). This was partly because they had complex societies for a longer time. They did not have the first humans, but they did have the first agriculture and the first civilizations. They had more domesticable plants and, very importantly, more domesticable animals. They also had those things for a longer time. This gave them more wealth and power than the Bantu had. They were also able to dominate South Africa where the Bantu could not because some of the crops that they had were able to grow in South Africa’s climate.
In these ways, we can see that climate and environment were the dominant factors in allowing the Bantu to dominate much of Africa and, later, in allowing the Europeans to be even more dominant than the Bantu.