Horizontal conflict is a major theme of the cliodynamics of Peter Turchin:
Turchin faces an uphill battle in creating his subset of psychohistory. But his initial results are interesting. Focusing on pre-industrial agricultural societies, Turchin argues that the primary reason for the rise of empires is an idea of Ibn Khaldun’s called asabiyah. Asabiyah is the “strong force” that gives a human group its ability to cooperate; it’s roughly equivalent to James Burnham’s “political formula”. Ibn Khaldun argued that the most productive environment for building asabiyah was a border community between nomads and farmers that was under constant threat of attack. This enhanced asabiyah often allowed the border community to defeat its enemies, then conquer them, and become an empire.
Turchin extends Ibn Khaldun’s idea by arguing that it’s specifically along “metaethnic frontiers” that empires arose. This is a frontier between societies that are not only diametrically opposed in means of production (e.g. pastoralist vs. agriculturalist) but diametrically opposed in culture as well. Some examples that Turchin offers are the frontiers between his native Russia and the Crimean Tatars, European Americans and American Indians, Han Chinese and Huns-Turks-Mongols-Manchus, Christian Spain and Muslim al-Andalus, Republican Rome and the Gauls, and Imperial Rome and the German tribes. The vast cultural differences between cultures bestride a frontier produce asabiyah more effectively than frontiers between people with a similar culture (e.g. the Franco-German frontier). This asabiyah is often sufficiently strong enough to make a political community along a metaethnic frontier expand into an empire.
For the forces that maintain asabiyah, Turchin points to studies based around the ultimatum game:
The ultimatum game is a game often played in economic experiments in which two players interact to decide how to divide a sum of money that is given to them. The first player proposes how to divide the sum between the two players, and the second player can either accept or reject this proposal. If the second player rejects, neither player receives anything. If the second player accepts, the money is split according to the proposal. The game is played only once so that reciprocation is not an issue.
These experiments seem to reveal three classes of people within any human group: knaves, saints, and moralists, as Turchin pointed out in his book War and Peace and War:
During the 1990s, several economists, most notably Ernst Fehr at the University of Zurich and his colleagues, decided to test the assumptions of rational choice theory experimentally…[and] what these experiments, and many others like them, reveal is that society consists of several types of people. Some of them — perhaps a quarter in experiments with American college students — are self-interested, rational agents — ‘the knaves’. These will never contribute to the common good, and will choose free-riding unless forced to [contribute] by fines imposed upon them. The opposite type, also about a quarter, are the unconditional cooperators, or ‘the saints’. The saints continue to contribute to the common pool and lose money, even when it is obvious to everybody that cooperation has failed (although most of them reduce the amount of their contribution). The largest group (40 to 60 percent in most experiments) are the conditional cooperators, or ‘the moralists’. The preference of the moralists is to contribute to the pot, so that everyone would be better off. However, in the absence of the mechanism to punish noncontributors, free-riding proliferates, the moralists become disgusted by this opportunistic behavior, and withdraw their cooperation. On the other hand, when the punishment option is available, they use it to fine the knaves [even though imposing a fine comes at a cost to them...and] the group [eventually] achieves the cooperative equilibrium at which, paradoxically, the moralists do almost as well as the knaves, because they now rarely (if ever) need to spend money on fining the free-riders.
It’s the moralists who maintain asabiyah:
The experiments also point to the key role of the moralists…. Self-righteous moralists are not necessarily nice people, and their motivation for the ‘moralistic punishment’ is not necessarily prosocial in intent. They might not be trying to get everyone to cooperate. Instead, they get mad at people who violate social norms. They retaliate against the norm breakers, and feel a kind of grim satisfaction from depriving them of their ill-gotten gains. It’s emotional, and it’s not pretty, but it does ensure group cooperation…. [Moreover,] that capacity for trust and moralistic punishment are wired into our brains. At some level, they are as basic as our abilities for finding food, or finding mates. It does not mean all humans will always behave in a cooperative manner. People are different…[and] societies differ in their ability to sustain collective action. But the capacity for cooperation (even if it is never exercised by many people) is part of what makes us human….[In addition,] as a result of our ability to use symbols, the idea of a social group (‘us’) has a peculiar grip on human imagination. Because of our psychological makeup, we tend to think of social groups, such as nations, as more ‘real’ than they are ‘in reality.’ And, because people treat nations as real, they behave accordingly and, paradoxically, make them real…Two key adaptations enabled the evolution of [human] ultrasociality. The first one was the moralist strategy: cooperate when enough members in the group are also cooperating, and punish those who do not cooperate. A band that had enough moralists to tip its collective behavior to the cooperative equilibrium outcompeted, or even exterminated, bands that failed to cooperate. The second adaptation, the human ability to use symbolic markers to define cooperating groups, allowed the evolution of sociality to break through the limits of face-to-face interaction, [and] the scale of human societies increased in a series of leaps.
Empires decline when asabiyah-driven imperial conquest brings wealth, security, and power. High asabiyah societies have strong vertical and horizontal cohesion and cooperation between elites and non-elites and within the elites and non-elites, fed by the moralists among the elites and non-elites. However, a great deal of asabiyah formation is driven by the pressure of external attacks. Imperial conquest can remove the immediate threat of external attacks. The lack of an immediate external threat leads to declines in asabiyah as elites and non-elites pursue divergent agendas and the influence of moralists decline. Elites tend to divide and that open opportunities for internal non-elites and external actors. This is what tends to push elites over the edge.
Loss of an elite doesn’t have to be a net loss. The rotation of elites is usually required to reinvigorate a society. However, the process is often unpleasant for everyone involved.