= Principle that asserts that internal cohesion is a function of outside threats: "it is the outside threat that counteracts the centrifugal tendencies within a kingdom ... Smaller-scale societies are much more likely to submit to the authority of a chief or king when they are threatened by hostile neighbors". 
From Peter Turchin, in his review of the book, the Creation of Inequality:
"Competition – not between chiefdoms, but at a higher level of social organization, between kingdoms (each a conglomerate of chiefdoms). In other words, it is the outside threat that counteracts the centrifugal tendencies within a kingdom. As Flannery and Marcus point out (following American anthropologist Robert Carneiro), “most societies do not surrender their autonomy willingly.” But smaller-scale societies are much more likely to submit to the authority of a chief or king when they are threatened by hostile neighbors.
It is unclear whether Flannery and Marcus treat this observation as a general principle, but if not, it amply deserves such designation. In fact, in sociological literature the proposition that external conflict tends to increase internal cohesion is known as the Simmel-Coser Principle (after German sociologist Georg Simmel and American sociologist Lewis Coser). What is particularly interesting is that in at least two archaeological cases, which Flannery and Marcus, there is clear evidence supporting the role of the Simmel-Coser principle in enabling the transition to state-level societies.
In the Oaxaca Valley the rise of the Zapotec state, with the capital at Monte Albán, put pressure on neighboring Mixtec societies, which “nucleated and fortified themselves to keep Monte Albán at bay; the resulting political consolidation allowed them to create embryonic kingdoms of their own.” Monte Albán itself was probably in military competition with an even larger state of Teotihuacan to the north.
Another, and even more striking example of the Simmel-Coser principle in action is the consolidation of the Moche state in Peru. Around 2,400 years ago the coastal valleys of Peru came under increasing raiding pressure from highly aggressive highland societies. During the first two centuries A.D. the highland raiders caused the abandonment of a number of coastal population centers. However, in one of the valleys the pressure from the highlands helped to consolidate indigenous population. The new Moche state succeeded in driving out the highland invaders and expanded to dominate fifteen coastal valleys. It seems likely that the external threat from the aggressive highlanders was a key factor in holding the Moche state together between 200 and 600 AD.” (http://peterturchin.com/wp-content/uploads/2019/02/FlanneryMarcus_review.pdf)