He argues that agonal relations are what drive philosophical change. This results in what he calls the "law of small numbers," meaning only a few sets of philosophies can emerge -- too few, and there are splits; too many, and there is synthesis. Agonal relations are what drive both.
But there is more to it than this that makes the idea Nietzschean. Nietzsche argued that societies with strong cultures were small and diverse, but with freedom of movement and cosmopolitan in nature. There had to be both conflict and an ability to move around freely and exchange ideas. But there could not be true uniformity, even if there was enough commonality to allow for the exchange of ideas. Nietzsche's ideals were the independent German states and the ancient Greek city-states.
The substantive contents of philosophy are different in China and Greece; the similarities are at the level of the network structure. In both the law of small numbers was operative early, as multiple factions emerged to fill the new intellectual attention space. In both cases the precipitating conditions involved political pluralism, the cosmopolitanism of commercial development and literacy, and a breakdown of traditional religious practices. (146)
He points out that the same is true of the development of ancient Indian philosophy as well (177).
If you want a vibrant development of philosophical ideas, you need political pluralism, the cosmopolitanism created by free trade and education, and a breakdown of the dominant world view. If you have increasing political unity, trade barriers, a less educated (in a real sense of high levels of learning vs. mere signalling) public, and a dominant world view, you are not going to have a vibrant philosophical community.
Nor are you going to have a vibrant artistic community. Consider the times when the Western arts became most creative: the tragic age of Greece, the Renaissance, and Modernism. Each were times of high political pluralism, free movement of goods and people, an emphasis on more widespread learning, and the breakdown of dominant ideologies. It is no coincidence that Modernism emerged in the aftermath of WWI.
Nietzsche argued that the strength of a culture is inversely proportional to the power of the government within that society. A strong government/political economy means a weak gift economy. The United States is facing a time of stagnant art, literature, and philosophy. It is no coincident that it is coinciding with a time when we are becoming more politically united (vs. the ideal political plurality of the 50 different states), with less economic freedom, where learning is being replaced with schooling-as-signalling, and where the political ideology is identical in the two dominant parties. The fact that we are generally disunited religiously is in fact a point in our favor. But we are practically all united in the religion of politics, where we try to emphasize false differences in order to justify our choice of tribe. We will have to reverse all these trends if we want a culturally vibrant, creative United States.