Perceptual grouping for war and peace

In international conflicts a land power is motivated to wage wars for expansion, but engaging in an enduring war is costly. Therefore, the decision of war and peace is of ultimate importance and has been studied intensively under game theory by analyzing pay-offs of different actions. Regarding such tension, we demonstrate that perceptual grouping, although completely irrelevant to those pay-offs, can nevertheless provide salient visual common sense as mutually acknowledged ‘rallying point’. Therefore, it significantly reduces the conflicts between powers, facilitating peace around the border of perceptual groups. To prove this, we designed a two-player game which highlights three fundamental principles of land power competition. Players’ wealth increases with expansion of lands. However, war is expensive even for the winner. Troops consume more supplies as they march away from capital. Players’ goal is not to annihilate the opponent but to acquire maximum wealth. Participants were divided into two groups. One played in a battlefield divided into two perceptual groups marked by colors, while the other’s battlefield is homochromatic without grouping. The colors were completely irrelevant to rules of the game. Compared with non-perceptual-grouping condition, more wealth is accumulated in perceptual-grouping condition with lower frequency of battle, indicating an eased tension overall. Players were more inclined to withdraw their troops from frontline for mutual benefits, manifesting weaker attack intention while reducing cost of supplies. This effect is largely implicit as almost all the participants failed to report the influence of color groups on their decisions. Our findings provide strong evidence that perceptual grouping as a purely visual phenomenon can nevertheless influence complex human conflicts. It suggests that the equilibrium of powers in the world may be implicitly and subtly influenced by humans’ perceptual grouping of territory.