that break-up has results which are of the very first importance in their bearing upon international pugnacity. The matter deserves careful examination. Professor William McDougal, in his fascinating work, "An Introduction to Social Psychology," says in the chapter on the instinct of pugnacity:
The replacement of individual by collective pugnacity is most clearly illustrated by barbarous peoples living in small, strongly organized communities. Within such communities individual combat and even expressions of personal anger may be almost completely suppressed, while the pugnacious instinct finds itself in perpetual warfare between communities whose relations remain subject to no law. As a rule no material benefit is gained, and often none is sought, in these tribal wars.... All are kept in constant fear of attack, whole villages are often exterminated, and the population is in this way kept down very far below the limit at which any pressure on the means of subsistence could arise. This perpetual warfare, like the squabbles of a roomful of quarrelsome children, seems to be almost wholly and directly due to the uncomplicated operation of the instinct of pugnacity. No material benefits are sought; a few heads and sometimes a slave or two are the only trophies gained, and if one asks an intelligent chief why he keeps up this senseless practice, the best reason he can give is that unless he does so his neighbors will not respect him and his people, and will fall upon them and exterminate them.
Now, how does such hostility as that indicated in this passage differ from the hostility which marks international differences in our day? In certain very evident